I ordered these to use with White Rose wheels I didn't want to lose. The WR axle needed 3/16" so the 4mm should have left some gap but wanted to try them. The axle diameter is bigger than 4 MM as they were too thick to go into the WR wheels. The axle is of good quality, The hole is very small so a nail or cotter pin cut in half may be used to retain the wheel.
Reviewed by: (Verified Buyer) Ben Thompson from Minneapolis on 10/12/2018