Ball Valve Stem Design:

The stem in a ball valve is not fastened to the ball. It commonly has a rectangular portion at the ball end that fits within a slot cut into the ball. The enlargement allows rotation of the ball as the stem is turned.

Ball Valve Bonnet Design

A bonnet cap fastens to the body that holds the stem assembly and ball in place. Adjustment of the bonnet cap permits compression of the packing that supplies the stem seal. Packing for ball valve stems is commonly in the configuration of die-formed packing rings generally of TFE, TFE-filled, or TFE-impregnated material. A few ball valve stems are sealed through means of O-rings rather than packing.