Polymer80's AR15 Universal Jig is compatibility with Mil-Spec 80 percent AR15 lower receivers no matter whether they're polymer or metal. The Universal Jig is designed with a super rigid long-fiber nylon composite, which allows you to utilize the jig up to 3 times. The jig also provides a stable platform for milling, and therefore encompasses the entire AR15 lower receiver. This kit includes a two sided jig, three trigger guides, 9mm HSS end-mill, and drill bits (5/16th, 3/8th, and 5/32nd).