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BB sizing(3 posts)

BB sizingixiz
Sep 28, 2001 5:48 AM
I understand there are two common BB threads
Italian and English they are both 24 tpi

What is the first number for the BB (on ordering)
68X102 & 73x102
What is the 68 and the 72, are they BB widths ?
And if so how do you know which to get for each frame ?
thanks
That's easy....Greg Taylor
Sep 28, 2001 5:54 AM
The first number is the width of the bottom bracket shell, in millimeters. The second number is the spindle width.

Generally, road bikes use a 68mm bottom bracket. The safest thing to do before ordering a replacement is to either measure the shell, or to just take out the old one and look at the size that is (usually) stamped on the cartridge.
oh myJack S
Sep 28, 2001 5:59 AM
BB 101:

First # is shell width- 68 is standard English and the one you forgot- 70- is Italian. 73 is oversize English (common on mtn bikes). If you know the shell width you will know whether it is Italian or English. Also, Italian threading is 36mm x 24, English 1.37" x 24. Spindle length depends on crank, frame clearance, and desired chainline.