# Bicycle Mechanics - 1 1/8 or 1 1/4 headset sizing

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View Full Version : 1 1/8 or 1 1/4 headset sizing

cs1
04-18-06, 06:28 PM
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

Svr
04-18-06, 07:23 PM
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.

cs1
04-19-06, 03:26 AM
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

cs1
04-23-06, 04:30 AM
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

DieselDan
04-23-06, 08:17 PM