Geissele Rifle Length Spring 42 in for AR-15/M-16. This unique spring design uses three independent strands of wire that acts as a harmonic damper and energy absorber by allowing the springs to flex separately from each other. This flex helps displace excess energy which decreases the chance of spring failure and assists with making your M-16/AR-15 rifle more reliable while diminishing the twang sound from the butt-stock. The Geissele M-16/AR-15 Super 42 Rifle Length Spring works with a standard rifle length buffer and buffer tube. Specifications for Geissele Super 42 Rifle Length Spring: Manufacturer: Geissele Finish: Type 3 Hard Coat Anodized Fabric/Material: Steel Gun Make: AR Platform Gun Model: M16 AR-15 Gun Type: Rifle Length: 42 in Weight: 10 oz Condition: New Package Contents: Geissele Super 42 Rifle Length Spring What firearm models does the manufacturer say Geissele Super 42 Rifle Length Spring is compatible with? The manufacturer says that Geissele Super 42 Rifle Length Spring is compatible with AR-15 M16Geissele 04-308-F: Rifle Length Spring 42 in for AR-15/M-16