JMac Customs ST-5 Skeletonized Tube for Compact M4 Stocks with Folding Mech Black. (With proper folding adapter) The ST-5 was designed specifically to allow stocks such as the LWRC Ultra Compact Stock to collapse all the way up to the folding mechanism for a shorter overall length and profile. The ST-5 is the perfect option for compact stocks and braces Attaching a stock to a pistol makes it an SBR and requires NFA approval. You are responsible for knowing and following your local/state/federal laws JMac Customs LLC is not responsible for the end users misuse of our products. Specifications for JMac Customs ST-5 Skeletonized Tube for Compact M4 Stocks with 1913 Folding Mech: Manufacturer: JMac Customs Color: Black Features of JMac Customs ST-5 Skeletonized Tube for Compact M4 Stocks with 1913 Folding Mech Integrated QD Sling Sockers 5" Length 5 positions Compatible with SIG folding mechanisms 7075 T6 Aluminum Type III Hardcoat Anodized FM-SM-1913 - 1913 Folding Mechanism Clamps on any "1913" or "Picatiny" Rail Works with all of our ArmBar Skeleton Stocks and Skeleton Tubes Works with SIG MPX/MCX folding braces/stocks Folds Left or Right Has 2 height adjustments 4140 HT Torque 20 in/lb. Adds approx .5" to stock/brace length Allows your stock/brace to lock in the folded position Fits most M4 style stocks/braces Lightweight and Rigid Package Contents: JMac Customs ST-5 Skeletonized Tube for Compact M4 Stocks with 1913 Folding Mech JMac Customs ST-5+FM-SM-1913: ST-5 Skeletonized Tube for Compact M4 Stocks with 1913 Folding Mech Black