This threaded adapter ring replaces the 2" eyepiece holder on the 2" 4x TeleVue Powermate Barlow and can only be used with the newest version of the Powermate (our part #9140C). After unscrewing the black 2" eyepiece holder from the chrome barrel containing the optics of the Powermate, the adapter threads directly onto the chrome barrel in place of the eyepiece holder. The adapter has T-threads th . . .