Inner barrel spacers for airsoft sniper rifles. Optimal for outer barrel inner diameter: 20mm. Made of durable polyacetal (POM) with two inner and two outer o-rings. Main purpose is to keep barrel in exact axle position. Less vibration, perfect axis = improove accuracy. Instalation doesn`t require any modification and is easy. But we suggest to apply silicone oil on the rubber o-rings. The outer diameter of the ring, including the rubber, is approximately 20.5 mm. It is therefore designed for barrels with a smaller diameter. For example, end of the barrel of VSR-10, BAR10, CM.701..etc. Two pieces in the packing.