Montana X-Treme Nylon Bristle AR Chamber Brush for Rifle 8/32 Thread .308/7.62mm 7175. 223/5.56 AR 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 a superior cleaning of lugs and chamber. Standard 8 x 32 thread. Specifications for Montana X-Treme Nylon Bristle AR Chamber Brush for Rifle: Manufacturer: Montana X-Treme Size: 18 x 32-33 Package Contents: Montana X-Treme Nylon Bristle AR Chamber Brush for Rifle Montana X-Treme 7175: Nylon Bristle AR Chamber Brush for Rifle 8/32 Thread .308/7.62mm