There are several mounting styles for potentiometers. The two most common are bushing mount and servo mount:

Bushing mount is the most common. With bushing mount, the potentiometer has a threaded bushing/collar around the lower portion of the shaft at the face of the potentiometer housing.

To mount the potentiometer one drills a hole in the panel where the potentiometer is to be mounted, slides the shaft/bushing through the hole and installs the supplied lock washer and hex nut onto the threaded bushing. Tightening it down fixes the potentiometer in place.

The Servo mount style, most frequently seen on single turn continuous rotation potentiometers, features a servo lid instead of a threaded bushing on the shaft end. For a servo mount potentiometer a hole is machined into the panel and the locating face of the potentiometer is inserted into the hole. Behind the locating face a larger lip extends out on the circumference of the potentiometer and seats against the back of the panel. Two or three mounting cleats then hold against the back of the lip holding the potentiometer in the panel from the rear. This method is recommended when the shaft is attached to a gear or other mechanism.