[admin]

Published: October 28, 2026  |  By YONGMAO Engineering Team

There is no ISO test that certifies a thru-axle on its own. The axle is approved as part of the frame-and-fork assembly under ISO 4210-6, which means a hollow axle can pass every laboratory test while the part that actually ships to your customers has never carried a load by itself.

Search for which ISO 4210 part covers thru axle fatigue test and every answer points to Part 6 — correct, and incomplete. The fork collects the fatigue cycles; the axle only appears as the thing the fork is bolted to. That gap is where field failures start: a fork that passed 1,500 N static bending on the lab's steel dummy axle, paired with a production axle whose wall thickness drifted 0.15 mm.

This guide maps the ISO 4210-6:2023 clauses that put force through an axle, gives the loads and cycle counts by bike category, and lists the thru axle inspection report measurements buyers should request before releasing a custom order from any China manufacturer.

1. Which ISO 4210 Part Covers Thru-Axle Fatigue, and Where Is the Axle Actually Loaded?

Part 6. ISO 4210-6:2023 is the frame and fork test method standard, and the only part of the series that bends an axle. Part 2 holds the requirements, Part 3 the common test methods, Part 5 steering, Part 7 wheels and rims, Part 8 pedals and drive, Part 9 saddles and seat posts. The axle sits between Part 6 and Part 7 and has no clause of its own.

It shows up instead as a load path in five places. Frame horizontal fatigue (4.4): city and trekking 100,000 cycles at 450 N, mountain bike 50,000 at 1,200 N, racing 100,000 at 600 N — the dropout-to-axle interface takes the reversal and thread fretting fails first. Frame drop-weight impact (4.1): 22.5 kg hammer from 180 mm for city, 212 mm racing, 360 mm MTB, measuring permanent dropout spread, which is axle bending set. Fork static bending (5.3): 1,500 N minimum in the EU type-approval table for L1e-A and L1e-B, applied through a test axle. Fork rearward impact (5.4): 180 mm for metal forks, 320 mm for composite, 360 mm MTB and 640 mm for racing composite, a retention test where the axle must still hold the hub. Disc-brake fork fatigue (5.6): 1,000 cycles at 100 ±5 °C, then 11,000 to 19,000 at ambient — the only case combining heat with a one-sided load.

Two numbers should drive your design. The MTB frame case is 1,200 N for 50,000 cycles, 2.7 times the city load at half the cycles, so one wall thickness cannot serve both honestly: city ends up over-built and MTB under-built. And in every fork test the laboratory mounts the fork on its own solid steel dummy axle, because the standard was written to qualify the fork. Your 7075 hollow axle is never the specimen.

This is the practical answer to which ISO 4210 part covers thru axle fatigue test: Part 6 qualifies the assembly, and the axle inherits a result it never earned. That is how two companies both claim "ISO 4210 tested" and ship very different parts. The standard is a gate for the frame builder, not a specification for the fastener. YONGMAO treats it that way: the YM12-AO-K carries ≥550 MPa tensile and ≥600 kgf bending, the YM15-AO-K more than 800 kgf, because those are the figures a brand can actually write into a purchase order.

✅ Bottom line: ISO 4210-6 loads the axle inside fork and frame tests but never certifies it, so component-level fatigue data has to be requested separately.

2. What ISO 4210-6 Leaves Untested, and What Replaces It?

Corrosion, socket torque and the geometry a fixture cannot see. No part of ISO 4210 sets a salt spray duration for a thru-axle, a breaking torque for the hex socket, or a concentricity tolerance for the bearing seats. Those three decide whether the part survives two winters and one over-enthusiastic mechanic.

Corrosion. Purchase orders usually phrase it as a thru axle salt spray test 336 hours requirement anodized to Type II — sulfuric anodizing at 15 µm ±5 µm, run to ASTM B117 at 35 °C, 5% NaCl, pH 6.5 to 7.2, 1 to 2 mL/80 cm²·h deposition. Type III hard anodizing at 50 µm and above reaches 500 to 1,000 hours. "Anodized" with no film thickness on the drawing is a colour, not a specification.

Socket torque. Install torque runs 10 to 15 N·m on a 12 mm axle and 6 to 10 N·m on a 12×100 front. A cold-formed YONGMAO hollow axle in 7075-T6 is validated to a 20 N·m socket breaking torque, only about 1.4:1 over the top install figure. That thin margin explains why a stripped socket is nearly always an over-torque event on an under-specified socket, not a bad heat lot.

Measurement. This is where buyer and seller talk past each other. Six numbers in a batch-level report end the argument: thread go/no-go on the stated pitch, P1.0, P1.5 or P1.75, with engagement at least 3 mm past the dropout width; bearing-seat concentricity to the thread axis within 0.05 mm on a dial indicator; straightness within 0.05 mm across the bearing span in V-blocks; wall thickness within ±0.1 mm on a sectioned sample; tensile to the 550 MPa line on a universal testing machine; and 336 hours of salt spray with no white corrosion on threads or bearing seats. The thru axle inspection report measurements buyers should request are these six, per batch, not per drawing and not a certificate with a logo on it.

One extra item costs nothing and proves more: the grain-flow photo on a sectioned sample. A machined axle shows cut fibres at the head-to-shank transition; a cold-headed one shows them flowing around the fillet, which is the whole reason fatigue life differs. Changzhou Yongmao Special Fastener Co., Ltd. has cold-headed fasteners since 1993 and still runs hollow parts through multi-station headers rather than turning them from bar stock, so that photo ships as a standard attachment instead of a favour. It is also the fastest way to tell a real factory from a trading company before you compare prices.

✅ Bottom line: Salt spray hours, socket breaking torque and a batch-level dimensional report cover the three failure modes ISO 4210-6 leaves open.

Frequently Asked Questions

Q: Which ISO 4210 part covers thru axle fatigue test — Part 6 or Part 7?

A: Part 6. Part 7 covers wheels and rims and tests the hub shell, not the axle, which is why the same word "fatigue" points at two different specimens. The axle is loaded as the fork-to-hub connection inside the Part 6 fork tests. If a supplier's report cites Part 7 for an axle, ask which fixture actually held the part.

Q: Is a short salt spray result enough to approve a batch?

A: No. A full run is 14 days of continuous chamber time and cannot be compressed. For samples, use 96 hours as a screening check, then confirm the thru axle salt spray test 336 hours requirement anodized on the first production batch, with film thickness measured on the same report. Presenting a 24-hour result as an equivalent tells you what the lab is worth.

Q: Can OEM axles come with component-level test reports?

A: Yes, and it belongs in the contract rather than in a favour. YONGMAO quotes custom thru-axles from a drawing or a sample, runs the six checks above on every batch, and supplies component fatigue and three-point bending data alongside the ISO 4210-6 fork report, so the brand can defend both the assembly and the part. OEM programs start from sample quantities, and the thru axle inspection report measurements buyers should request are quoted back with your own tolerances filled in.

Next Step

Send your axle drawing — diameter, length, pitch, material and target salt spray hours — and YONGMAO (Changzhou Yongmao Special Fastener Co., Ltd.) returns a factory quote with the test plan attached: which ISO 4210-6 clauses apply to your frame category, plus the six batch measurements at your tolerances. Samples in about a week, reports with every shipment.

Start from the bicycle front and rear thru-axle range, or open the YM15-14-K hollow thru-axle for the base specification.

http://www.yonmach.com
Changzhou Yongmao Special Fastener Co., Ltd.

[Author]

Posts