1/4 NPT allen pipe plug. Chrome

NPT threads are -self sealing- since they are slightly tapered the diameter slowly becomes bigger towards to top. - 13.5mm is the approx. diameter of this plug in the middle of the plug including the thread itself. Note: For easier identification of the correct plug the diameter (approximately measured in the middle of the plug including the thread itself) is given in millimeters. Note: Pipe plug sizes are totally different when compared to common US bolt sizes.