Fast and loose pulleys
|(Mach.)||two pulleys placed side by side on a revolving shaft, which is driven from another shaft by a band, and arranged to disengage and reëngage the machinery driven thereby. When the machinery is to be stopped, the band is transferred from the pulley fixed to the shaft to the pulley which revolves freely upon it, and vice versa.|
See also: Fast
Webster's Revised Unabridged Dictionary, published 1913 by G. & C. Merriam Co.