The handwheel on the Kenmore Model 158 sewing machine has a shiny knurled knob in the middle:
Turning the knob clockwise screws the knob inward and clamps a friction clutch that locks the handwheel to the main shaft; the motor belt drives the handwheel, the handwheel drives the shaft, and the shaft drives everything inside the sewing machine.
Remove the small screw, turn the knob counterclockwise to remove it, and you see the clutch:
Yes, the black stamped metal part is the clutch.
Those three projections around the exterior limit the knob’s travel to a bit under 1/3 turn, with the little screw you just removed traveling between two of the projections. When you reinstall the knob:
- Turn it until it’s snug
- Insert and tighten the screw
- Done!
The two dogs in the middle project outward from the shaft notches: the bases engage the notches, the tips bears on the knob’s inner surface. Tightening the knob compresses the dogs, presses the clutch against the handwheel, and locks everything together.
It’s entirely possible to install the clutch backwards and, while it’ll come pretty close to working, it’s not quite right.
The Smell of Molten Projects in the Morning 
Ah! One of my round-tuit projects (pushing 20 years in “progress”, alas) is to finish the telescope mount and drive. I’ve needed a clutch, and this looks like a fair idea to steal. Bookmarked!
It’s one of those simple and effective mechanisms that’s obvious when I see it, but that I would never figure out on my own…
The screw is removed, but the clutch doesn’t seem to be engaging the hand wheel. The two will turn independently, but they won’t turn together when the pedal is pressed. How many times will i have to turn it clockwise to re-engage it?
Basically, turn until it stop turning! That will press the knob firmly against those little tabs and engage the clutch. The knob has about four turns of the thread, but once you get to the end, it’ll seem very sensitive.
That little screw ensures you can’t back it off more than 1/3 turn, which is all you need: the clutch requires less than 1/3 turn to go from “completely loose” to “completely tight”.