They are both variable resistors that control the amount of volume or how loud a pickup will be when plugged into an amplifier and the tone control usually rolls the high end off a pickup or combination of pickups. On passive instrument that require no pre-amp or power boost in the circuit the values are usually 250 k audio taper for Fender Strats, Tele's, P-Bass, J-Bass etc., and Gibson uses 300 k audio taper pots and 500 k audio taper for vintage Gibson's. Fenders have been known to use 1 Meg. ohm pots on their instruments.
On most Fender instruments, solid and knurled split shaft pots are used for volume and tone controls. Fender Stratocasters use three knurled split-shaft potentiometers. The knurled shaft keeps the pressure fit knob from spinning beyond 10 on the dial. Telecaster knobs use a tightened set screw to keep it from spinning on the solid shaft. Fender Jazzmasters use two nylon Stratocaster volume and tone knobs pressed on to the solid shaft pot and would often become loose with extensive use.
Older Gibson knobs are pressure fit on the knurled split-shaft and after time the plastic on the knob shrinks making it difficult to remove or the knob splits and cracks. The contacts inside the potentiometer should be occasionally lubricated with a specific cleaner and lubricator made especially for contacts and pots. Never use WD-40 as some have used and never use oil or grease to lubricate switches as they can cause shorting and a mess inside your instrument.
WRITTEN ON JUNE 12, 2015, BY