No thread is required for installing press-fit fluid level sight glasses.The fluid level sight glass is inserted into the bore. By simply tightening the ring nut using the pin key, the seal is pressed against the contact surface which, at the same time, holds the sight glass in position. For removal, reverse the procedure. Application is limited to non-pressurized or slightly pressurized tanks. Maximum heat resistance: 80° C (175° F). Dimensions vary per model.