Bought not for a bass but as the lower part of a dual-concentric knob on a custom amp. In this application it’s almost impossible to find the dimensions of the knob and determine whether it, and the existing top knob will fit. Try to find this information yourself - what a job! I’m writing this review just to provide this information and hopefully make it more accessible to search engines.
The bottom outside diameter is 27,7mm (1,01”). The knob width/height is 8,9mm (0,35”).. The diameter of the top indentation is 19,2 mm to fit a top knob of 19mm (0,75”), diameter snugly inside it.. Basically it’s a 1” bottom knob to fit a 3/4” top knob.
The knob comes with a Torx grub screw (they didn’t always) and fitted my potentiometer shaft only after a little gentle filing with a round needle-point file for a snug fit. I guess this wouldn’t be an issue for it’s intended use on a Fender bass.
Anyway it looks great and does the business. It’s a solid product which I happen to find a bit spendy. The laws of supply and demand I suppose. It is a good knob using all criteria by which you would judge one :)