1 1/8 or 1 1/4 headset sizing
 

I was looking to replacing my son's Trek MTB headset. The locknut is marked 25.4 but the threading is way larger than any 1" quill I've seen. Now I find out it could be 1 1/8 or 1 1/4" How can I tell which it is? Virually no LBS's carry either one in the area. Thanks

Tim

If the quill of the stem measures 1" exactly, the bike is equipped with a 1 1/8" headset. Another way to tell is to measure the distance between the flats on the top nut of the headset -- genrerally 1" = 32mm, 1 1/8" = 36mm, 1 1/4" = 40mm.

1 1/8" is a very common MTB headset size. I'm suprised none of your local shops stock it.

Thanks for the info the actual quill is " and it uses a mm wrench. Problem is I didn't know exactly what size it was. I appreciate the help.

Tim

Problem solved. I called around and found a LBS that had steel locknuts in black for $3 ea. He saved me taking off the headset and fork race to replace the entire unit. That old aluminum locknut stripped out real fast. Thanks for the replies.


Tim

1 1/4" headsets are usually Cannondale Headshocks.