Frame and bearings
Which headset fits your frame: four measurements to a headset code
Two head tube bores, the cup type at each end and two fork diameters decide which headset fits. This page turns readings like 44.0mm and 55.9mm into the S.H.I.S. code headset makers list, shows which fork numbers finish it, and flags what to check before you order.
The short answer
If the cups that came out of your frame held the bearings inside the head tube, the frame is a ZS44 at the top and a ZS56 at the bottom: 44.0mm names a 44, and 55.9mm names a 56. The fork finishes the code. With a tapered fork (1-1/8 inch where the stem clamps, 1.5 inch at the crown), order ZS44/28.6 | ZS56/40. With a straight 1-1/8 inch fork, order ZS44/28.6 | ZS56/30, a lower cup that steps the 56mm bore down to a 30mm crown race.
Check each end on its own. If either cup sat outside the head tube, that end is EC instead, EC44 at the top or EC56 at the bottom, with the same fork numbers after the slash. The traps below explain why the type matters.
Order by the code, not by the bike's model year. Park Tool's summary of the system says headsets from different brands with matching codes interchange and fit the same bikes, and its table of ZS pairings calls ZS44/28.6 | ZS56/40 the common tapered configuration. Cup depth and stack height, covered below, are the details the code can leave out.
Of the three makers' listings in the table below, Cane Creek's is the one that carries both codes as complete headsets. Hope's Pick'n'Mix page sells top and bottom cups separately, and its charts go from head tube and steerer diameter to a part number; its technical guide labels cup 2 as ZS44/28.6 and cup E as ZS56/40. Chris King's InSet 2 page gives the tapered code only.
| Maker and listing | ZS44/28.6 | ZS56/40 (tapered fork) | ZS44/28.6 | ZS56/30 (straight 1-1/8 inch fork) |
|---|---|---|
| Cane Creek Forty | Complete headset BAA0533K; lower half only BAA0090K | Complete headset BAA0585K; lower half only BAA0089K |
| Hope Pick'n'Mix cups | Top cup HSC2 + lower cup HSCE | Top cup HSC2 + lower cup HSCL, or HSCE with the HS136 crown converter |
| Chris King InSet 2 | Listed as ZS44/28.6, ZS56/40 | Not listed on the InSet 2 page |
What the code is made of
The Standardized Headset Identification System (S.H.I.S.), which Cane Creek and Park Tool also call the Headset Code, was announced in a release dated November 9, 2010. The companies leading its development included Acros, Cane Creek, Hope, Race Face, Reset and Ritchey. It needs four dimensions: the fork's stem-clamp diameter, the fork's crown-race seat diameter, and the head tube's top and bottom inside diameters. Two letters in front of each half say where the bearing sits:
- EC (external cup): bearings in cups outside the frame.
- ZS (ZeroStack, also called semi-integrated or internal): bearings in pressed-in cups, with cup and bearing inside the head tube.
- IS (integrated): no cup. The bearing sits directly in a bonded or machined seat that is part of the frame, and it lifts out by hand.
Each half reads type, bore, slash, fork diameter: the stem-clamp diameter on the top half, the crown-race seat on the bottom half. The top half is written first, with a vertical bar between. The spec's own examples are EC34/28.6 | EC34/30 (traditional 1-1/8 inch) and ZS44/28.6 | ZS44/30 (1-1/8 inch ZeroStack).
Matching a reading to a size
The numbers are names, not measurements. The 2010 sheet footnotes its diameters as rounded for naming, and Park Tool calls them a code rather than an exact measurement. That is why a 43.97mm bore is a 44. Plain rounding fails for some sizes: the 1.5 inch bore of 49.57–49.61mm is a 49, not a 50, and Park Tool notes that the 29.8mm bore of 1 inch JIS headsets is EC29.
| Bore as measured (mm) | Name | Headset types |
|---|---|---|
| 30.05–30.10 | 30 | EC or ZS |
| 33.90–33.95 | 34 | EC or ZS |
| 36.90–36.95 | 37 | EC or ZS |
| 41.35–41.40 | 41 | EC or ZS |
| 43.95–44.00 | 44 | EC or ZS |
| 49.57–49.61 | 49 | EC or ZS |
| 55.90–55.95 | 56 | EC or ZS |
| 38.15–38.25 | IS38 | Integrated |
| 41.10–41.20 | IS41 | Integrated |
| 41.95–42.05 | IS42 | Integrated |
| 47.00–47.10 | IS47 | Integrated |
| 49.10–49.20 | IS49 | Integrated |
| 52.05–52.15 | IS52 | Integrated |
Your 44.0mm sits at the top edge of the 44 range and your 55.9mm at the bottom edge of the 56 range. Sources differ by a few hundredths: Park Tool's table gives 43.90–43.95mm for a 44 bore, and Hope's head tube drawing gives 43.95mm plus up to 0.05mm. Measure each bore in two directions and average the readings, as Park Tool advises, then take the named size your reading points to.
Whether a cup will hold depends on the cup as well as the bore. Hope draws its ZS44 top cup at 44.10mm and its ZS56 lower cup at 56.05mm, each plus up to 0.05mm. Against your 44.0 and 55.9, that works out to 0.10–0.15mm and 0.15–0.20mm of press fit, inside the 0.1–0.25mm that Park Tool calls adequate. Park Tool warns that 0–0.05mm may be weak. Published cup sizes differ: Park Tool's table lists 44.1mm and 56mm cups for these codes, which against your readings works out to 0.10mm each, the low end of that range. Park Tool's method is to measure the outside of the cups you are about to press and compare them with the bore. Do that before pressing anything in, especially if your bore reads larger than its named range.
Measure the fork as well
The fork sets the numbers after the slashes, which is why the frame alone can't settle the order: Cane Creek lists both a 56/40 and a 56/30 lower for the same bore. Measure the steerer where the stem clamps; a 1-1/8 inch steerer is 28.6, and the 2010 sheet gives 28.45–28.6mm. Then measure the crown-race seat, the shoulder at the base of the steerer, with the crown race off. Cane Creek's Headset Code Break Guide says to round that reading to the nearest whole millimeter, though its online guide to identifying headsets says to round it up. The 2010 ranges settle it: a 40 seat is 39.79–39.85mm and a 30 seat is 30.015–30.075mm.
| Fork steerer | After the top slash | After the bottom slash |
|---|---|---|
| Straight 1 inch | 25.4 | 26 |
| Straight 1-1/8 inch | 28.6 | 30 |
| Straight 1-1/4 inch | 31.8 | 33 |
| Straight 1.5 inch | 38.1 | 40 |
| Tapered 1-1/8 to 1-1/4 inch | 28.6 | 33 |
| Tapered 1-1/8 to 1.5 inch | 28.6 | 40 |
If you would rather not pull the crown race, look for the steerer entry in the fork maker's specifications for your fork model, or in the bike's spec list. A fork described as tapered 1-1/8 to 1.5 inch converts to 28.6 and 40. For the frame, check the technical specifications or frame specs section of the bike maker's page for your model. Cane Creek notes that some brands publish the headset code there, and many do not.
Traps that give the wrong code
- Measuring with the cups still in. Take the stem and fork off first, as Cane Creek's guide says you will most likely need to, and look at what holds each bearing. If a bearing sits directly on a seat in the frame, that seat is part of the frame and is not removed in headset service (Park Tool). Only pressed-in cups come out: Cane Creek names Park Tool's RT-2 or an equivalent cup remover for driving them out, and says it is needed only when a press-fit headset is installed. Then measure with all bearings and cups removed. Inside a cup you would be measuring the bearing seat: Cane Creek's ZS44 cups take a 41mm bearing and its ZS56 cups a 52mm bearing, numbers that look like the integrated IS41 and IS52 sizes.
- Guessing the letters. Park Tool lists EC and ZS cups for the same 44 and 56 bores, so the bore can't tell you the type. Look at each end, or at what came out of it: a bearing in a cup inside the head tube is ZS, a bearing in a cup outside it is EC, and no cup at all is IS. The two ends can differ; Cane Creek's guide calls ZS at the top with EC at the bottom a common pairing on steel and titanium frames. Switching type changes the height. Cane Creek's help article gives a 44mm head tube as an example where a ZS or an EC lower both work, with less stack height from the ZS, and its Forty listing puts ZS lowers at 4mm and EC lowers at 12mm.
- Measuring an integrated seat too deep. The seats are angled, so Cane Creek says to measure at the very edge of the opening.
- Near-miss sizes. ZS55 is a separate, rarer lower at 54.90–54.95mm (Park Tool), and Cane Creek and Hope list cups for it. A 55.9mm reading is a 56.
- Cup depth. The code doesn't carry it. Park Tool notes that insertion depth varies by brand, and a frame designed for a shallow cup will not properly fit a deeper one. Hope's drawing for a 44/56 head tube shows the 43.95mm top bore running at least 9.5mm deep and the 55.90mm lower bore at least 10mm. Measure how far each of your bores runs at full diameter from the end of the head tube, and compare. Cane Creek's Forty listing and Chris King's InSet 2 page give no depth, so ask the maker before ordering; Chris King's page sends fitment questions to a King dealer or its customer service.
- Proprietary frames. Cane Creek's Headset Code Break Guide says it does not apply to proprietary designs some bike makers use. If your headset looks like none of the three types, ask the frame maker.
Stack height and your spacers
Stack height is how much of the steerer the headset occupies. It is optional in the code, written as H plus millimeters. Cane Creek lists its Forty ZS tops at 8mm or 15mm and its ZS lowers at 4mm, which works out to 12mm or 19mm for a ZS44/ZS56 pair. Hope lists 8mm for cup 2, including three shims, and 6mm for cup E, which works out to 14mm. Hope's page gives no figure for cup L, or for cup E with the HS136 converter.
Compare the new total with the headset you are replacing; Park Tool's steering column sizing article shows how to measure each half. If the new headset is taller, take that much spacer height out from under the stem. If it is shorter, add spacer height: Park Tool says the stem or a spacer should sit about 3mm above the top of the steerer, and headset adjustment is impossible if they are flush with it or below it.
If a taller headset leaves no spacer to take out, the top of the steerer ends up that much lower inside the stem. Park Tool says a carbon steerer must go all the way through the stem, with a spacer on top. For any steerer, check the fork and stem makers' instructions for how far below the top of the stem the steerer may sit before you ride.
Before you order and install
Cane Creek's Headset Code Break Guide says a full code describes a complete headset that comes with the bearings, cups and crown race you need; stem spacers are sold separately. Cane Creek's complete Forty assemblies also include the top cap, preload bolt, top cover and compression ring, but no star nut. Hope sells its cups as separate top and bottom parts, and its Pick'n'Mix page lists the Head Doctor top cap as sold separately, so check what each cup listing includes. If only one half is worn, both makers sell halves: Cane Creek lists the Forty ZS44/28.6 top alone with a tall cover (BAA0079K) or a short cover (BAA0080K), and its lowers are in the table above.
Cane Creek recommends professional frame preparation and headset installation. Park Tool warns that a cup more than 0.3mm larger than the bore may be very difficult to install and frame damage may result, and says to check with the manufacturer before reaming or facing a carbon frame.
The same measure-then-match approach settles press-fit bottom brackets and freehub bodies.
Check it on your own equipment
These take you to the manufacturers and standards bodies the page draws on, so you can look up your exact model.
- Manufacturer specification
Cane Creek Forty headset: both codes as complete headsets (opens in a new tab)Pick 'ZS/ZS - Complete' under Type & Position, then '44/28.6 | 56/40' (part BAA0533K) or '44/28.6 | 56/30' (BAA0585K) under Head Tube Size & Steerer Tube Size. The page also lists top-only and bottom-only halves, stack heights, what each complete headset includes, and a link to the Headset Code Break Guide. — www.canecreek.com - Manufacturer specification
Hope Pick'n'Mix cups: charts for tapered and straight forks (opens in a new tab)Hope's cup range, stack heights for the cups it lists, and linked upper and lower charts that go from head tube and steerer diameter to a part number: 44mm with a 28.6mm steerer is HSC2, 56mm with a 40mm steerer is HSCE, and 56mm with a 30mm steerer is HSCL or HSCE with the HS136 converter. — www.hopetech.com - Standards reference
Park Tool: Standardized Headset Identification System (Headset Code) (opens in a new tab)Tables of bore, cup and crown-race sizes for the common EC, ZS and IS codes, and worked examples including ZS44/28.6 | ZS56/40 and a straight-fork reducer. — www.parktool.com - Official support page
Park Tool: Head Tube Reaming and Facing (opens in a new tab)How to measure a head tube's inside diameter with a caliper and compare it with the cups, the press-fit ranges Park Tool works to, and its caution for carbon frames. — www.parktool.com
What this page does not tell you
- Makers' published bore ranges differ by a few hundredths of a millimeter. If your reading sits at the edge of a range, check the drawing or listing from the maker of the cup you plan to buy.
- The code does not include cup insertion depth, and Cane Creek and Chris King publish none for these headsets. Measure how deep each bore runs at full diameter and ask the maker before ordering.
- Hope's cup and bore drawings date from 2011. Check its current upper and lower charts for part numbers.
- Hope gives no stack height for cup L, or for cup E used with the HS136 converter, so you can't work out the spacer change for those in advance.
- This page covers the industry-standard EC, ZS and IS types. A frame with a proprietary headset needs the frame maker's answer.
Sources
16 documents, each with the facts on this page it supports. Manufacturers revise specifications, so every source is dated — open it before you buy.
- A 44.0mm top reading and a 55.9mm bottom reading fall in the 44 and 56 bands, so a frame whose cups held the bearings inside the head tube is ZS44 at the top and ZS56 at the bottom.
- A tapered 1-1/8 to 1.5 inch fork takes 28.6 after the top slash and 40 after the bottom slash; a straight 1-1/8 inch fork takes 28.6 and 30.
- The S.H.I.S. release is dated November 9, 2010, and says the companies leading its development include Acros, Cane Creek, Hope, Race Face, Reset and Ritchey.
- Four dimensions determine fit: the fork's stem-clamp diameter, the fork's crown-race seat diameter, and the head tube's top and bottom inside diameters.
- EC (external cup): bearings are contained in cups located outside the frame.
- ZS (semi-integrated or ZeroStack): bearings are in pressed-in cups, and cup and bearings rest inside the frame.
- IS (integrated): bearings fit directly into a bonded or machined interface integrated into the frame, with no cup.
- In a complete code the top headset is listed first and the lower second, separated by a vertical bar; the upper half ends in the stem-clamp diameter and the lower half in the crown-race seat diameter.
- The spec's examples are EC34/28.6 | EC34/30 (1-1/8 inch traditional) and ZS44/28.6 | ZS44/30 (1-1/8 inch ZeroStack).
- The 2010 sheet footnotes its diameters as rounded for naming convention.
- A 43.97mm bore falls inside the 43.95-44.00mm range named 44.
- Plain rounding of the 49.57-49.61mm bore would give 50, yet the sheet names it 49.
- Press-fit head tube bore ranges and names: 30.05-30.10 = 30; 33.90-33.95 = 34; 36.90-36.95 = 37; 41.35-41.40 = 41; 43.95-44.00 = 44; 49.57-49.61 = 49; 55.90-55.95 = 56.
- Integrated head tube bore ranges and names: 38.15-38.25 = IS38; 41.10-41.20 = IS41; 41.95-42.05 = IS42; 47.00-47.10 = IS47; 49.10-49.20 = IS49; 52.05-52.15 = IS52.
- The sheet names the press-fit bore sizes for both EC and ZS types.
- Fork sizes in the code: straight 1 inch 25.4/26; straight 1-1/8 inch 28.6/30; straight 1-1/4 inch 31.8/33; straight 1.5 inch 38.1/40; tapered 1-1/8 to 1-1/4 inch 28.6/33; tapered 1-1/8 to 1.5 inch 28.6/40.
- The 28.6 (1-1/8 inch) threadless stem-clamp diameter has a range of 28.45-28.6mm.
- Crown-race seat diameters: 39.79-39.85mm is named 40; 30.015-30.075mm is named 30.
- A ZS56/30 lower pairs the 56mm bore with a 30mm crown race, acting as a reducer for a straight 1-1/8 inch fork, as Park Tool describes for its ZS49/30 reducer example.
- If either cup sat outside the head tube, that end is EC: Park Tool lists EC44 and EC56 codes, and each half is written type, bore, slash, fork diameter.
- Park Tool's summary says that if two brands have matching SHIS descriptions, they will interchange and fit the same bikes.
- Park Tool's table of possible ZS combinations lists ZS44/28.6 | ZS56/40 as the common tapered configuration.
- Park Tool says S.H.I.S. is also known as the Headset Code.
- Park Tool calls the ZS type the internal headset, also Zero Stack or semi-integrated.
- Park Tool says the IS bearing holder is part of the frame and is not removed as part of headset service, and the cartridge bearing is lifted out for replacement.
- Park Tool says bore numbers are a code, not an exact measurement; the 1 inch JIS bore is 29.8mm but its code is EC29.
- Park Tool's tables list a 43.90-43.95mm bore for EC44 and ZS44, and 55.9-55.95mm for EC56 and ZS56.
- Park Tool's ZS table lists a 44.1mm cup for ZS44 and a 56mm cup for ZS56.
- Park Tool's listed cup sizes against readings of 44.0mm and 55.9mm work out to 0.10mm of press fit each, the low end of its adequate range.
- Park Tool lists ZS55 as a rare 1-1/2 inch semi-integrated size with a 54.90-54.95mm bore.
- A 55.9mm reading falls in the 56 range, not the 55 range.
- Park Tool says stack height may be added to the code as H followed by millimeters, and stack height is the amount of fork column the headset occupies.
- Park Tool's SHIS article has tables for EC, ZS and IS codes and worked examples including ZS44/28.6 | ZS56/40 and a ZS44/28.6 | ZS49/30 reducer.
- The code can leave out cup depth and stack height: stack height is optional, and cup insertion depth varies by brand.
- Park Tool notes low-profile cup insertion depth varies between brands and types, and a frame designed for a shallow cup will not properly fit a deeper cup.
- Of the three listings used (Cane Creek Forty, Hope Pick'n'Mix, Chris King InSet 2), only Cane Creek's carries both ZS44/28.6 | ZS56/40 and ZS44/28.6 | ZS56/30 as complete headsets.
- Cane Creek lists the Forty ZS/ZS Complete 44/28.6 | 56/40 as part BAA0533K.
- Cane Creek lists the Forty ZS/ZS Complete 44/28.6 | 56/30 as part BAA0585K.
- Cane Creek lists Forty ZS bottom-only halves 56/40 (BAA0090K) and 56/30 (BAA0089K), so it offers both a 56/40 and a 56/30 lower for the same bore.
- Cane Creek lists the Forty ZS44/28.6 top alone with a tall cover (BAA0079K) or a short cover (BAA0080K).
- The Forty listing splits each variant across selectors named Type & Position and Head Tube Size & Steerer Tube Size, with a Part Number field.
- Cane Creek states ZS44 cups take a 41mm bearing and ZS56 cups take a 52mm bearing.
- The 41mm and 52mm bearing sizes inside ZS44 and ZS56 cups resemble the integrated IS41 and IS52 names.
- Cane Creek lists Forty stack heights of 8mm or 15mm top and 4mm bottom for ZS, and 16mm top and 12mm bottom for EC.
- Cane Creek lists a Forty ZS bottom in 55/40 (BAA0737K).
- Cane Creek's Forty listing gives no cup insertion depth.
- Cane Creek's Forty ZS figures work out to 12mm (8 + 4) or 19mm (15 + 4) for a ZS44/ZS56 pair, and Hope's cups 2 and E to 14mm (8 + 6).
- Cane Creek's complete Forty assemblies include top cap, preload bolt, top cover, compression ring, bearings, crown race and cups (if applicable), and no star nut.
- The Cane Creek Forty page links a Headset Code Break Guide.
- Hope's Pick'n'Mix page sells top and bottom cups separately.
- Hope lists stack heights of 8mm for cup 2, including 3 shims, and 6mm for cup E.
- Hope's Pick'n'Mix page gives no stack height for cup L or for cup E used with the HS136 converter.
- Hope's Pick'n'Mix page lists the Head Doctor top cap as sold separately.
- Hope's Pick'n'Mix page links its Upper and Lower Headset Compatibility Charts and its Headset Technical Guide.
- Hope's charts go from measured head tube diameter and steerer size to a Hope part number.
- Hope's lower compatibility chart maps a 56mm head tube with a 40mm steerer to HSCE, and with a 30mm steerer to HSCE + HS136 or to HSCL.
- Hope's lower chart lists cups for a 55mm head tube (HSCG).
- Hope's upper compatibility chart maps a 44mm head tube with a 28.6mm steerer to part HSC2.
- Hope's technical guide labels cup 2 as S.H.I.S. ZS44/28.6, cup E as ZS56/40, and HS136 as a 1-1/8 to 1.5 inch lower steerer crown converter.
- Hope's drawing for its ZS44/28.6 cup (Hope 2) gives a cup diameter of 44.10mm (+0.05/0) and a head tube bore of 43.95mm (+0.05/0).
- Hope's drawing for its ZS56/40 cup (Hope E) gives a cup diameter of 56.05mm (+0.05/0) and a head tube bore of 55.90mm (+0.05/0).
- Hope's cup sizes against bores of 44.0mm and 55.9mm work out to 0.10-0.15mm and 0.15-0.20mm of press fit.
- Hope's drawing for a tapered 44/56 head tube shows the 43.95mm top bore at least 9.50mm deep and the 55.90mm lower bore at least 10mm deep.
- Chris King lists the InSet 2 as ZS44/28.6, ZS56/40, designed for a 44mm/56mm tapered head tube and a 1-1/8 to 1.5 inch tapered steerer; no ZS56/30 version appears on that page.
- Chris King's InSet 2 page gives no insertion depth and asks buyers to confirm fitment before ordering, sending fitment questions to a King dealer or its customer service.
- Cane Creek calls the codified headset name the Headset Code.
- Cane Creek says integrated-style bearings need no pressing and are fitted into the head tube by hand.
- Cane Creek's Ultimate Guide says the bottom steerer measurement is rounded up to the whole mm.
- Cane Creek notes some bike makers publish the headset code in the technical specification or frame specs sections of their websites, and many do not.
- Cane Creek says you will most likely need to remove the stem and fork to see the headset type.
- Cane Creek names Park Tool's RT-2 or an equivalent cup removal tool, needed only to measure a head tube with a press-fit headset installed, and says to remove all bearings and cups before measuring.
- Cane Creek says to check the headset type at top and bottom separately and calls ZS|EC a common combination on modern steel and titanium frames.
- Cane Creek says to measure an integrated head tube at the very edge of the opening because angled seats give incorrect readings if the calipers go too deep.
- Park Tool says to check head tube inside diameter in two different directions and average the readings.
- Park Tool considers 0.1-0.25mm of press fit adequate and says 0-0.05mm may be weak and allow movement.
- Park Tool says to measure the outside of the headset cups to be pressed and compare with the head tube inside diameter.
- Park Tool warns a pressed cup more than 0.3mm larger than the frame inside diameter may be very difficult to install and frame damage may result.
- Park Tool says the reaming and facing processes are intended primarily for metal frames and to verify with the manufacturer first for carbon frames.
- Park Tool's reaming article covers measuring head tube inside diameter with a caliper and comparing it with the cups.
- Cane Creek's Headset Code Break Guide says to measure the bare head tube top and bottom and round to the nearest whole mm, measure the steerer top precisely, and measure the steerer bottom with no crown race installed, rounded to the nearest whole mm.
- Cane Creek's Headset Code Break Guide identifies ZS as a bearing housed in a cup inside the head tube, EC as a bearing housed in a cup outside the head tube, and IS as a bearing housed directly in the head tube with no cup.
- Cane Creek's Headset Code Break Guide says it identifies industry standard headsets and is not applicable to proprietary designs used by some bike makers.
- Cane Creek's Headset Code Break Guide says a full headset code describes a complete headset that comes with the bearings, cups and crown race needed; stem spacers are sold separately.
- Cane Creek's help article says a press-fit head tube's bare inside diameter should be measured top and bottom with calipers, in millimeters.
- Cane Creek's help article says a ZS44/30 lower and an EC44/30 lower both work on the same 44mm press-fit head tube, and the ZS lower has less stack height.
- Park Tool's steering column sizing article describes measuring the lower and upper stack of a headset separately.
- A taller headset needs that much spacer height removed from under the stem, and a shorter one needs spacer height added, because stack height is the length of steerer the headset occupies.
- If a taller headset leaves no spacer to remove, the stem rises by the stack difference, so the top of the steerer sits that much lower inside the stem.
- Park Tool says the stem or spacers should sit about 3mm above the top of the steerer, and if they are flush with or below it, headset adjustment is impossible.
- Park Tool says that when a new part changes stack height, the spacers need to be rearranged accordingly, adding or removing spacers to reach the right height.
- Park Tool says a carbon steerer must go all the way through the stem, with a spacer on top of the stem.
- Park Tool advises double-checking with the manufacturer for specifications and compatibility, since incompatible components can be a safety hazard.
- Cane Creek's Forty EC/ZS installation guide recommends professional frame preparation and headset installation.