Differential or transmission cooler: 149 to 1270 micron. This filter needs to protect the cooler passages from clogging.
Engine oil pre-filter (inspecion filter): 40 to 1270 micron. This filter needs to protect the suction side of the pump from damage.
Engine oil main filter: 8 to 40 micron. Crankshaft journals are often finish-polished using 23 micron abrasives.
Fuel system pre-filter (before the pump): 25 to 400 micron. This filter only needs to catch larger particles to prevent the final filter from clogging prematurely.
Fuel system final filter (after the pump): 1 to 74 micron. High-performance fuel injector manufacturers recommend a 10 micron or finer filter.
General rules of thumb:
For any given size, a coarse filter will flow better than a fine filter. This is why coarse filters are usually recommended for thicker fluids. Increasing the filter size can (partially) compensate for the lower flow of a finer filter.
In any application, it is hard to go wrong with a coarse pre-filter followed by a fine filter. The fine filter protects the machinery, and the coarse filter protects the fine filter from clogging too quickly. Installing the coarse filter before the pump will also protect the pump from damage.