GrovTec US 0.25in Machine Sckrew Locking Swivel Set Black. Requires modifications to gas block on current models. Set includes one pair of GT Locking Swivels. Specifications for GrovTec US 0.25in Machine Sckrew Locking Swivel Set: Manufacturer: GrovTec US Color: Black Gun Type: Rifle Gun Model: Universal Package Contents: GrovTec US 0.25in Machine Sckrew Locking Swivel Set 0.75in Wood Screw 0.25in Machine Screw 1 pair GT Locking Swivels Spacers 10-32 Hex Nut GrovTec US GTSW13: 0.25in Machine Sckrew Locking Swivel Set Black