Drop-in accuracy fix! Stops annoying movement between receiver halves. One of the fastest, easiest, cheapest accuracy-improvements you ll ever find for your AR-15 Tough, high-density synthetic material wedge drops into the space behind the takedown pin in the lower receiver to provide tension between the receiver halves and prevent movement for improved accuracy. Takes the loose gun factor out of the equation, so you shoot tight, consistent groups. Can be trimmed to accommodate any variation in upper-to-lower receiver fit.