Abstract: Methods and interface devices for attaching to a firearm muzzle a suppressor having a rearward end with a threaded portion. The interface device includes an elongated body portion having a first end portion, a second end portion generally opposite the first end portion. The body portion defines a bore therethrough, and the bore defines a longitudinally-extending central axis. The first end of the body portion defines a threaded engagement portion configured to threadingly engage the threaded portion of the firearm muzzle. The exterior surface of the body portion defines visible indicia indicating a preselected position, whereby upon the suppressor being threadingly engaged with the threaded engagement portion and rotated such that the rearward end suppressor is at a preselected position relative to the indicia, the suppressor is properly tightened with respect to the interface device.