Evolution Gun Works Rock Island BBR 3.10in barrel .45ACP Guide Rod Kit Black. The head of the guide rod has smooth beveled edges to make for a seamless look. All kits are drop-in. This guide rod kit is made for the Rock Island BBR 3.10" .45ACP. This kit uses a 1/4" diameter guide rod flat wire ISMI spring and our fully machined reverse plug. In independent testing ISMI spring have endured in excess of 100000 compression cycles. We dont recommend going that long between changes however. With an ISMI spring practice routine maintenance and change it once a year. Specifications for Evolution Gun Works Rock Island BBR 3.10in barrel .45ACP Guide Rod Kit: Manufacturer: Evolution Gun Works Color: Black Package Contents: Evolution Gun Works Rock Island BBR 3.10in barrel .45ACP Guide Rod Kit Evolution Gun Works 10495: Rock Island BBR 3.10in barrel .45ACP Guide Rod Kit Black