Shower knobs typically connect to the water valve control in one of two ways: with a screw through the center of the knob on the end or with a worm screw on the side. With repeated use, the shower knob may loosen as the screw works loose against the valve control. As long as the shower knob is not worn out, the knob can be tightened in a few minutes using basic tools.
Turn off the shower and inspect the knob to determine how it is attached to the valve control. A worm screw in the side of the knob where it slides onto the valve control will require an Allen wrench, also called a hex key, to tighten it. A screw on the end of the knob in the center can be tightened with a screwdriver.
Pop off any plastic cap on the knob where the screw is located. Some shower knobs include a cap over the screw for a better appearance. The cap may be labeled with an H or C to denote hot or cold water. Save this cap.
Insert the tip of a screwdriver into the screw's head on the end of the shower knob, or place the long end of an L-shaped Allen wrench in the hole on a side-mounted screw.
Push the knob in firmly on the valve control while turning the screwdriver or Allen wrench clockwise until tight.
Replace the protective cap over the screw and push the cap to lock in place.