British ('58 Patt.) GSR Water Bottle Stopper. New. Black.
Very tough and durable Brit-issue spare water bottle cap.
This is the later-issue - GSR - variant, designed to accompany the drinking facility of the newer gas mask - general service respirator.
This is the cap only and will fit all issue osprey bottles made over the last 50 years or so!
Note: no gas mask or water bottle is included.