An early industrial millwrighting component consisting of a cast-iron hub and rim with rectangular slots cut into its face. Wooden blocks, usually made of dense hardwood like hornbeam or hickory, are driven into these slots to act as gear teeth. This hybrid construction ran quieter than all-metal gears and allowed operators to easily replace broken teeth instead of casting a whole new wheel.
Heard on the job
The old grist mill still uses a mortise wheel to transfer power from the water shaft to the grindstones.