Great Price! These knobs fit like a glove on 1/4" smooth shaft pots.
The flat head set screw is set inside the plastic of the knob. Slide them on your Alpha's and tighten gingerly. No need to make them crazy tight. They'll hold for a long time. (Do you get a bit rambunctious with a screwdriver in hand? I recommend buying a few extra in case you strip that screw! Having a bit of crazy glue on hand isn't a bad idea, either.)
Measurements are 1/2" at the base and 5/8" tall for a 1/4" shaft.