The 1-1/4" diameter Crank Knob was made by multiple manufacturers, namely Raytheon, the JAN Hardware Company, and DAR Electronics Inc.
The crank knobs are mounted on the top area of the Crank Generator. In Ghostbusters they were grey, but were replaced with a black version (possibly painted) in Ghostbusters 2. This is sometimes a good way to identify which movie the pack is from; however some packs from the first movie were repainted and reused.
The knob fits on a 1/4" shaft, and is secured in place with 2 brass set screws.
The Raytheon knob product line and JAN Hardware Company has been acquired by the Electronic Hardware Corporation (EHC). The crank knob is part of the [b]MS91528[/b] Military Series of "spinner" knobs. It has found its way to several familiar applications, but the most household friendly has been the MRC model train power transformers. However, be advised: some transformers come with incorrect knobs that are simply cheap knockoffs of the real thing.
Grey Knob at EHC Part Number MS91528-3S2G (Flat Grey Knob)
Black Knob at EHC Part Number MS91528-3S2B (Flat Black Knob)
Some part numbers associated with the Grey Crank Knobs:
-124B4MC -3S2G -KMS12S2LGRAY -MS91528-3S2G