This (3) piece Armorer's kit is a must have for the home builder looking to build up a new rifle, or service their existing weapon. The upper vise block fits standard mil spec 5.56 upper receivers, and securely holds it in place without damaging or marring it. The lower vise block fits into either the top or bottom of the 5.56 magwell and locks into place wiith the mag catch. This unique feature allows you to work on the top or bottom of the lower receiver as needed. The armorer's wrench provides solutions to work on a 5.56 free float hand guard barrel nut, flash hider, and castle nut. As an added bonus, it also features the tool to install an AR10/.308 free float hand guard on the other side.