There are plenty of AR-15 vise blocks on the market designed to fit into the magazine well of your gun's lower receiver. However, due to the wide variation in dimensions from manufacturer to manufacturer, these blocks rarely hold any AR-15 securely. The Real Avid Smart-Fit Vise Block is designed to eliminate the rattle and movement of these one-size-fits-all blocks, thanks to its expanding design. To ensure a solid, immovable fit inside the Real Avid Smart-Fit AR-15 Vise Block, simply insert the block into your gun's magazine well and rotate the adjustment handle until tight. This ensures a secure mounting point that allows your rifle to be held in place while work is performed. In addition to traditional, vise-mounted work, this Real Avid Smart-Fit Vise Block also works on inverted lower receivers, allowing users to work on pistol grips, trigger guards and other components on the bottom of the receiver with ease. This block also includes the company's Pivot Lock, which allows users to access the barrel and chamber of their guns, hands-free.