Clock and Instrument Cleaning Brushes Bristles are available in varying degrees of hardness for cleaning and dusting clocks, instruments, and parts. Hard bristles for extra heavy grit. Soft bristles for more delicate parts and removing dust. Bristles measure 4 1/2" long, 5/8" deep. Overall length 10 1/4". You can choose from 4 different types of Bristles: Hard, 1/2 Hard, 1/2 Soft and Soft.