Introducing the new SI Tribus Make sure your weapon is clear Start by taking down the upper receiver Remove the stock Remove the buffer and buffer spring Package includes: 1.5mm Hex Key M3 X 25mm set screw Castle Nut and End Plate. Use a 2 inch Spanner Wrench or a standard AR tool to unscrew castle nut. Disassemble the buffer tube by unscrewing existing castle nut. Remove the detent spring While unscrewing the buffer assembly, make sure to hold the buffer retainer pin. Remove the buffer retainer pin and spring Finish unscrewing the buffer tube assembly and remove the end plate and castle nut Start installing the Tribus Castle Nut Put on the Tribus end plate Screw the assembled buffer tube to the lower receiver. Put the buffer retainer pin and spring back into place and continue screwing the buffer tube. Put the detent spring back on. Hand tighten the castle nut Use spanner wrench to fully tighten Screw on the provided M3 x 25mm set screw in the threaded hole located on the side of the Tribus.