Bristle Brush Features Montana X-Treme Bronze Bristle Shotgun Cleaning Brushes will tackle the toughest cleaning operations - including plastic wad residue - with ease. Bristles are heavy duty bronze on a brass core for confidence against accidental marring of the bore. 5/16 x 27 thread. Bristle Brush Specifications Montana X-Treme Bronze Bristle Brush for Shotguns 5/16 x 27 Thread 12 ga