Metolius Bouldering Brush An indoor brush, perfect for keeping plastic holds clean. Originally designed to clean the internals of an M-16 rifle. Designed originally to clean the interal parts of an M-16 rifle, the Metolius Bouldering Brush is the perfect piece of equipment to clean you items. The two different head sizes ensure that you can get into those tighter spaces making sure your gear is well cleaned. The super-stiff bristles further enhance the cleaning properties of this product.