06MORB HOLLOW HEX PLUG

Blocking off unused ports on manifold blocks is exactly the kind of job this plug handles well. The O-ring boss thread form gives you a reliable seal without a lot of fuss, and the hollow hex body lets you drive it in with a standard hex key even when clearance is tight. Brennan Industries builds these to hold up in working industrial conditions, so you're not going to have to babysit it once it's seated.