The Top Adapter just slides in from the top of the receiver.
The adapter should slide in smoothly with a very close fit. The outside dimensions of the adapter are machined to match the profile of a Mil-Spec magwell.
It does not have a bolt actuator built in. You can add a 9mm bolt catch over the top of it for that feature. A high quality Colt or equivalent part is recommended as poor copies can break.
