Abstract: A coupling member (20) includes cylindrical body (22) and hook (24). Sleeve (70) slides over the outer surface of body (22) between and open position (as shown) and a closed position and carries pin (50) which is guided by slots (60,62) formed in body (22). Closure shaft (30) is mounted within body (22) and biased by spring (42) towards a closed position wherein end (32) of shaft (30) is received within recess (44) formed in portion (26) of hook (24). Pin (50) is slidably mounted in transverse bore (56) of shaft (30). Spring (58) biases pin head (52) towards shaft (30) so that when shaft (30) is in the closed position, pin head (52) is seated in recess (66) and shaft (30) is thereby locked in the closed position. Coupling member (20) can be used for securing lines in mountaineering or cave diving.