Hold your receiver securely in the vise without damage. Precisioin machined in the USA from a solid block of high density polymer gives it a good snug fit. In addition to being a very durable tool it will not scratch your receiver. You can hold a "bare" receiver because it has a machined workstop on the side. Just snap the vise block in like you would a magazine and its good to go. Our hammer fall test block is held in place by the forward takedown pin. Hammer can be safely tested without damaging the lower.