JMac Customs ST-7 Skeletonized Tube for Compact M4 Stocks with Folding Mech Black. (With proper folding adapter) Some M4 style stocks use tension tabs designed for standard buffer tubes to mitigate movement. These will work on our Skeletonized Tubes however you may experience some wiggle. Requires a mount or folding mech to install 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. FM-SM-1913 - 1913 Folding Mechanism JMac Customs LLC is not responsible for the end users misuse of our products. Specifications for JMac Customs ST-7 Skeletonized Tube for Compact M4 Stocks with 1913 Folding Mech: Manufacturer: JMac Customs Color: Black Package Contents: JMac Customs ST-7 Skeletonized Tube for Compact M4 Stocks with 1913 Folding Mech JMac Customs ST-7+FM-SM-1913: ST-7 Skeletonized Tube for Compact M4 Stocks with 1913 Folding Mech Black