I'm totally ignorant in this area, and probably didn't know how to properly google my question - sorry..

I found this specification here: (https://si.shimano.com/pdfs/ev/EV-RH-IM10-2045B.pdf). My guess is that M10 is the about the metric thread specification (https://en.wikipedia.org/wiki/ISO_metric_screw_thread). But what is the meaning of B.C. 3/8" then?

Another question about this spec: (https://si.shimano.com/pdfs/ev/EV-FH-2200-2202B.pdf) - what would be the meaning of 6-11/32" - it can't be a range, or can it?


It looks like the hub axle has two different threads on it: M10 probably in the middle and 3/8" either side of the middle section. Not sure what the "B.C." refers to.

enter image description here

This is confirmed by the fact that the hub nuts (1), which go on the extremities are 3/8", whereas the lock nuts (18), which go on the middle section, are M10.

I think 6-11/32"means 6 inches and (or plus if you prefer) 11/32 of an inch. Indeed, if you do:

(6 + 11/32) * 25.4 = 161.77mm

and the spec says 161mm. You can apply the same logic for 16mm and 6-17/32:

enter image description here

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