Real Avid Smart Fit Vise Block, Fits AR15/AR10, Compatible with Most Vices, Gray AV1015SFVB The Smart-Fit AR15 Vise Block and Vise Block Sleeve for AR10" DPMS LR-308 and SR-25 is the best lower receiver vise block you'll ever use. Magwell sizes have a notoriously wide range of tolerances" and traditional blocks create wiggle and wobble on a gun vise. Smart-Fit's design solves that. It expands to fit all MIL-SPEC AR15s" AR10s and similar magwells" making loose" sloppy-fitting blocks a thing of the past.