The Geissele Magazine Well Reaction Block solves a problem every armorer runs into eventually: how do you hold a lower receiver still without marring the finish or fighting it with one hand while working with the other? Slide it into the mag well, clamp it in a bench vise, and the receiver stays locked in place while both hands stay free for the actual work. Machined from 6061-T6 aluminum with a wear-resistant clear anodized finish, this Geissele Reaction Block is built to hold up to repeated shop use without degrading. Integrated slots make starting M-LOK fasteners fast, and multiple orientation positions let the block index for access from the top or bottom of the receiver - useful whether the task at hand is a buffer tube installation or general lower assembly. It's built to fit both AR-15/M4 and AR-10/SR25 platforms, so one block covers most of what's likely to come across an armorer's bench. This Geissele Mag Well Vise Block is manufactured and finished in North Wales, Pennsylvania, the same facility that produces Geissele's triggers and rifle components - so the fit and finish match the standards of the guns it's built to service. Key Features: Machined from 6061-T6 aluminum Wear-resistant clear anodized finish Slides into mag well, clamps directly to a bench vise Integrated slots for starting M-LOK fasteners Multiple orientation positions for top or bottom access Fits AR-15/M4 and AR-10/SR25 lower receivers 6" length, 3" width, 1.56 lbs Manufactured and finished in the USA A dedicated Geissele AR-15 Reaction Block like this one turns a two-handed fight into a one-tool solution - the kind of shop fixture that earns a permanent spot on the bench once you've used it. Geissele Automatics Geissele Magazine Well Reaction Block 02-2781