noun
also idle wheel
: a wheel or roller used to transfer motion or to guide or support something: as
a. : idler gear
b. : idler pulley
c. : a rubber-surfaced roller in a sound-recording or sound-reproducing mechanism for transferring power by frictional means (as from the motor shaft to the turntable rim in a phonograph)
[s]idlerwhe.jpg[/s] [
idler wheel 1
]