Bottom bracket spindle length I have a square taper (JIS) Shimano UN-55 bottom bracket with dimensions 68mm (shell width) and 110mm (spindle length) on my single speed (chainline 42-44mm).
Can a set of Stronglight JIS track crank arms (107mm axle length) be fitted to my BB (110mm spindle length), or must the axle length of a crank arm match the spindle length of the bottom bracket?
If the cranks can be fitted, how is the chainline affected?
Axle length and spindle length are the same thing.
Three-piece cranks typically specify a required axle/spindle length to achieve a specific chain line, I.e. how far away the chain rings are from the center plane of the frame.
An axle/spindle longer or shorter by x millimeters will move the cranks x/2 millimeters outboard or inboard respectively.
Some manufacturers are very good about specifying axle/spindle length for individual crank models. Some provide a recommended bottom bracket model from which the length can be found, others provide no information at all.