noun
tapper
TAP-er/tˈæpɝ/
A person or device that strikes lightly or repeatedly.
The triangle's tapper strikes the suspended metal lightly with a slender rod.

Etymology
Tap is ultimately imitative of a light rapping sound. Adding -er names the person or device producing that sound by striking lightly.
More examples
- She is a constant foot tapper when music plays.
- The small tapper strikes the bell at regular intervals.
- A felt cover keeps the tapper from striking too loudly.
Forms
tapper · tappers
tap verb — To strike lightly, often with a sound.
Similar words
- knocker
- Usually knocks on a door, often to attract attention.
- striker
- Delivers a blow that need not be light or repeated.