PS ergal ball bearing spring guide for gear box MARUI M4 SRE next gen (GM4S). Upgrade your plastic spring guide to the FPS ergal ball bearing spring guide for gear box MARUI M4 SRE next gen. Plastic spring guides can break easily, especially on upgraded guns. If you want your airsoft gun to outshine the competition, you absolutely need a metal spring guide. The ball bearings on this model are especially good for upgraded guns because they help reduce tension on the spring by allowing it to spin freely, thus reducing the probability of the spring breaking. Each FPS spring guide is made of ergal and it is also anodized for smooth surface finish. The shape of the rim makes it compatible with most of the springs today on the market. It increases the speed of the ball by 2/3 meters per second. 100% MADE IN ITALY