Please read before ordering:

HK builds the roller-delayed housings to a general spec, but there's real part-to-part variation in the trunnion/housing interface, so fitment on things like handguards, lower receivers/housings, and stock adapters can run anywhere from a hair loose to noticeably tight depending on the specific gun and the specific part.

A few things that are generally true here:

• HK-pattern housings (like B&T, PTR, Zenith, or aftermarket lowers) are made to interface with the roller-delayed trunnion, and since HK's own tolerances aren't razor tight, aftermarket makers have to design around a tolerance range rather than one exact dimension.
• Loose fit usually shows up as wobble or rattle at the housing pin/trunnion interface. Tight fit usually means the housing won't fully seat, or the pins are hard to push in/out.
• Shims, different pins, or light stoning/fitting by someone who knows the platform can often fix minor tightness or looseness without needing a full custom fit.
• For anything beyond minor adjustment, having an HK-experienced smith hand-fit the housing to that specific gun is the right call, especially if you're chasing a true lockup with no play.