The reversible engine pulley for the 5 or more H.P. garden tractor has a reversible outer sheave. This sheave can be turned around to give either a 2-1/2 or 3-1/4 effective outside diameter for power take off work, with a section A belt only. This is done by removing the three cap screws from the outer end of the pulley and assembling the reversible sheave to obtain the desired effective (larger)) O.D. (narrow groove) with the rotary mower 917575123 and 917575124, weed cutter 917575126, and tri cut rotary mower only.

Warning: do not use narrow groove 3 1/4" O.D. (A belt) with cordwood saw 917575108, rotary mower 91757594 and 96, and cutter bar 91757569.

(Taken from the rotary lawn mower manual)