Rock River Arms M4 Stock Wrench Features The Rock River Arms M4 Stock Wrench is machined from steel and finished with a parkerized coating for corrosion resistance and long service life on the workbench. Measuring 7-5/8 inches long it is sized to give the leverage needed to properly torque a castle nut without slipping or marring the receiver extension. The three-lug spanner design engages the A4-style castle nut squarely letting the user hand tighten it to the receiver with confidence that it will stay put under recoil. This non-slip fit takes the guesswork out of stock installation and prevents the rounded-off nuts that come from using improvised tools. Beyond the castle nut spanner the rubber-coated handle includes a cutout shaped to fit the receiver extension tube allowing quick removal of an A1 or A2 style stock as well. The rubber coating makes the tool comfortable to grip and turn even when applying significant torque during a stock swap. This universal fit works across AR-15 platforms making it a practical addition to any home armorer s toolbox. Builders upgrading from a fixed A1 or A2 stock to a modern A4 collapsible stock will find this wrench handles both ends of that job cleanly. Rock River Arms M4 Stock Wrench Specifications Brand: Rock River Arms Fits: AR-15 Universal Material: Steel Finish: Parkerized Length: 7-5/8 Available At: GrabAGun