This modification of the single-bevel 20-tooth gear was
intended to offer some new possibilities rather than to
replace it. These possibilities include the ability to rotate
freely on an axle so that the gear can be used to transfer
drive “over” the axle without driving it and without adding the
axle’s friction to its own. The new gear also has a half-studthick
collar at its base, which makes it remain on the axle
more securely. It is much less likely to snap than the singlebevel
20-tooth gear, but it can act only as an idler gear.