I can only theorise, although I've used a screwdriver to self adjust with the shoes on the axle after replacing the cylinders.
In the image.......when the footbrake and or handbrake is applied.......the pivot point, left end, moves "North East", and rotates clockwise.
The smaller section has to react so moves in anti clockwise around the "drill pivot" and so the "heel" on the top right presses against the shoe, and the knurled edges rub against each other just hard enough to click one tooth, thus holding the shoe just a bit further from the cylinder, and closer to the drum.
How's that sound?
