Shimano FH-RM40-8 135mm Rear hub

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Hub Data
Manufacturer Shimano
Model FH-RM40-8
Position Rear
Axle Type 10mm
OLN 135 mm
Spoke Interface Type J-Bend
Brake Compatibility rim brake
Drive Interface Shimano 8/9/10/DynaSys (34.95mm)
Internal Gearing none
Dynamo Type none
Spoke Hole Diameter 2.6 mm
Left Flange Diameter 45.3 mm
Right Flange Diameter 45.3 mm
Left Flange Offset 35.8 mm
Right Flange Offset 19.8 mm
Mid-Flange Offset -8 mm (to the left)
Weight 373 g
Hub ID 272
Record Status Public
Created Feb 24, 2014 1:15pm
hub dimension diagram
PLEASE NOTE: Shimano publishes hub dimensions in a relatively confusing manner on They seem to provide the outside-to-outside flange spacing, and an overall offset of the flanges as a whole. Wheelbuilders are interested in the distance from the midpoint between locknut faces to the middle of the flange (not the inside or outside face). When necessary, I convert Shimano's data into useful spoke calculation dimensions with some simple arithmetic, and factor in 3mm thick hub flanges (an approximation). The formula is to divide spacing by two, add or subtract the overall offset, then subtract half of our assumed 3mm flange thickness. Please check the notes to see if the values for this part are derived from Shimano's published data or actual measurements of a hub specimen. -Karl
A very inexpensive cassette hub with virtually no bearing seals. Not made to be pretty or durable. -Karl

9/9/19 -- I think this entry is for what is actually the FH-RM40-8 (with an 8/9/10 freehub body). Updating model name and entering a new record for the FH-RM40 (7spd freehub body) that I have on hand to measure and doesn't quite match these offsets. I suspect the two are the same base hub shell but with a different freehub body and left side axle spacers, hence the nearly-identical model names. -Karl