The 90 degree swivel attaches between the regulator second stage and its low pressure hose, routing the hose down the diver's chest and/or under the arm, which increases comfort and streamlining. This low-profile adapter is not an omnidirectional swivel and so it maintains its angle and will not allow the regulator to flop around. Sidemount divers use the right angle swivel to route their hoses down their chest to the bottles eliminating the need to route the hose around the neck. The replacement O-ring for this adapter is size 010.