British SR 6 Service Respirator
The British SR 6 Service Respirator consisted of a black rubber facepiece with a large speech diaphram, and 40mm filter that attached directly to the cheek. Both of these examples have their filter port on the right cheek to accomodate left handed soldiers. The top one was made by Avon in 1969. The second set of images shows a left handed SR6 made by Leyland & Birmingham Rubber, paired with a British Armored Fighting Vehicle Helmet.
Similar masks in my collection: Turkish SR 10