Nylon Bristle AR Chamber Rifle Brush Features Montana X-Treme .308/7.62mm Chamber Brushes are constructed on a brass core with very stiff heavy bristles that will not flatten and retain their memory like brass chamber brushes from other manufactures. Designed for superior cleaning of lugs and chamber. Standard 8 x 32 thread. Nylon Bristle AR Chamber Rifle Brush Specifications For .308 and 7.62 Standard 8 x 32 thread Brass core Stiff bristles