Tapper
WordNet
noun
(1) A dancer who sounds out rhythms by using metal taps on the toes and heels of the shoes
(2) Someone who wiretaps a telephone or telegraph wire
(3) A worker who uses a tap to cut screw threads
(4) A person who strikes a surface lightly and usually repeatedly
"Finger tappers irritated her"
(5) A tavern keeper who taps kegs or casks