Tiger Rock AR-15 Rifle Length Buffer Tube Assembly. The extra heavy-duty bolt catches on the end of the buffer tube to help secure it in the event that it is removed or spooked. These buffer tube assemblies are to be used with standard buffers and standard buffer springs and may require slight tuning of the buffer and/or buffer spring weights for use with new or "lightened" weight" buffers and/or spring weights. Package Contents: Tiger Rock AR-15 Rifle Length Buffer Tube Assembly Tiger Rock TBS-L: AR-15 Rifle Length Buffer Tube Assembly (T-L B-LB S-L)