GrovTec US Non-Rotating Flanged Base Black. It's held in place on the inside of the stock by a mating panel nut. Features an extra durable matte Black Nitride Finish. Specifications for GrovTec US Non-Rotating Flanged Base: Manufacturer: GrovTec US Color: Black Fabric/Material: Stainless Steel Finish: Nitride Threads per Inch: 1/2x28 Features of GrovTec US Non-Rotating Flanged Base Stainless steel construction non-rotating flanged base for hollow stock Easily secures in place with 3 set screws Includes retainer nut for stable installation on hollow stocks Package Contents: GrovTec US Non-Rotating Flanged Base GrovTec US GTHM196: Non-Rotating Flanged Base Black