Motor Dia.

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Well-Known Member
Jan 18, 2009
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Could some tell me the Dia. of motor cases? I know that a 38mm is 1.500 but what is a 24, 29, and a 75? I would apprectate this info
A 24 is 24mm, a 29 is 29mm, etc. Divide mm by 25.4 to get inches. Are you sure you're asking the right question? Those numbers ARE the diameters.
I thought maybe he wanted to know if they were over/under sized relative to that dimension, as in "fits in a 24mm ID tube" vs "24mm OD".
Oh yeah, that's possible too... I think its english because when he said he knew 38 is 1.5. However, it certainly could be that.. Come to think of it, I don't know the answer. Is it a 29mm OD motor?
Well, I just checked my 13/18/24mm engines with a dial caliper, and they're pretty much dead on the mm measurement. BT IDs seem to be a few thou over. I don't have anything bigger than 24mm, but the 29mm and 38mm BTs at are also oversized.
Yes, to get inches, divide by 25.4.
29mm would be 1.142, 24mm is .945 and 18mm is .709, 38mm is 1.496
for BT sizes, (id&od) go to and print the page and pin it up on the wall.