Brass Core and Bronze Bristles (Benchrest Type) Designed for competition shooters to withstand frequent use. Construction consists of a high quality brass core and coupling with bronze bristles. Pro-Shots Benchrest Quality Brush has been used for many years with several world records to its credit. This bore brush is exceptional for bore cleaning with superior cleaning ability and it will not harm the bore. All Pro-Shot Benchrest Bore Cleaning Brushes have a specific size for each caliber with each brush being oversized for extended life. American Standard #8-32 thread.