How To Measure Thru Axle For Bike Trailer Uk
Before you order any 12 mm trailer thru-axle adapter, remove the stock rear thru axle and record three numbers: diameter, overall shaft length (from the base of the head to the tip of the threads), and thread pitch. Hub spacing labels such as 142 mm or 148 mm are not the same as axle length, and ordering from spacing alone is a common UK buying mistake.
Why hub spacing is not axle length
Many frames list rear hub OLD (over-locknut dimension) as 142 mm or 148 mm. Trailer adapters are sold by the physical length of the axle shaft that replaces your stock axle so a hitch plate can sit outside the dropout. UK retailers commonly list trailer thru-axle lengths around 160–178 mm for those hub families, and they still warn you to confirm pitch with the bike maker. Treat spacing as a clue, not a substitute for a tape measurement.
Fit guides from trailer brands ask you to identify head shape, pitch and measured length when moving a hitch onto a thru-axle bike — see the Thule UK trailer fit guide for the measurement mindset, not as a brand-specific shopping list.
Step checklist: measure once, write it down
- Remove the stock rear axle with the wheel supported so the hub cannot drop. Keep the OEM axle nearby as a reference.
- Note head/seat shape — flat or conical (tapered). You will need the matching seat style when spacers are involved; see our guide on flat versus conical thru-axle spacers.
- Measure diameter across the smooth shaft (most modern disc gravel, road and MTB rears are 12 mm). Non-12 mm ends need a different hitch path.
- Measure overall shaft length from the underside of the head to the tip of the threads. Do not include the head height in that length figure.
- Identify pitch from markings on the axle (for example M12x1.5) or with a 1:1 printed pitch guide. UK hire and retailer guidance expects you to distinguish 1.0, 1.5 and 1.75 before buying — summarised in Adventure Kit Hire's thru-axle adapter advice.
- Photograph the markings and the ruler reading so a shop can confirm if anything is ambiguous.
Decision table: map numbers to a trailer axle window
| What you measured | What to do next |
|---|---|
| 12 mm diameter + pitch clearly M12x1.0, 1.5 or 1.75 + length in a common ~160–178 mm trailer-adapter window | You can compare pitch-matched trailer axles; UK Burley-channel listings often sit in that length band for 142–148 mm hubs (Fawkes Cycles Burley thru-axle listing). |
| Pitch unclear or unmarked | Stop and confirm at a bike shop before ordering — mismatched threads can damage the frame. |
| Fat-bike / very long axles (often ~209–229 mm) or non-12 mm diameter | Do not force a standard 12 mm trailer adapter window; follow the trailer maker's long-axle or solid-axle path instead. |
| 142/148 known but length not measured | Measure length anyway — OLD is not shaft length. |
For pitch families in plain language, read M12x1.5 vs M12x1.75 trailer thru-axle pitches after you have a number on paper.
Who should pause
- Fat-bike or other long axles outside the common trailer-adapter length window.
- Anything that is not a true 12 mm thru axle (quick-release skewers and some hub-motor solid axles follow other hitch kits).
- Damaged dropouts, seized axles, or unmarked shafts when you cannot get a shop confirmation.
After the measurements match
Only when diameter, pitch and length line up with a listed 12 mm trailer axle option should you compare live product choices. On this site the pitch-matched SKUs are collected on the ThruSports 12 mm thru-axle adapter detail page. If you still need the wider trailer-axle context, the ultimate UK bike trailer thru-axle guide covers the hitch story at overview level.
Finish with a short pre-ride check from the UK bike trailer hitch safety checklist before the first loaded trip.