Mauser Drum Bung, S70x6 (69mm) OD with 6mm pitch buttress thread with 3/4″ (20mm) BSP insert fitted. Clear or Light Blue PE O-ring (sometimes black rubber O-ring).
German Mauser bungs are easily identified because they have an O-ring under the thread. Most other bungs have a flat gasket at the top of the thread under top flange.
 BSP insert plug fitted with PE O-Ring){kind=link}