Hold your AR receiver securely in the vise without damage. This lower vise block has magazine latches on both sides so the lower vise block can be installed from the top or bottom. Precisioin machined in the USA from a solid block of high density plastic gives it a good fit, durable and will not scratch your receiver. You can hold a "bare" receiver because it has a machined workstop on the side. Another nice feature is the rifle with bolt installed can be held in a vise, just snap the vise block in like you would a magazine and its good to go.