9mm thread adapter - Stern Defense 1/2-36 to 1/2-28 thread adapter Muzzle Device

Like a prior review i saw, this productvwas covered with surface rust in package. Not a good look. It also has a weird unthreaded section on the inner part of 1/2×28 thread that does not allow a flush fit thus requiring a washer which seems like a recipe for a baffle strike. Thankfully this has not happened but it made me nervous.