United Shield Gas Mask Strap GMStrap. This chemlight strap is used for training exercises and contains a spare o-ring that keeps the strap from chafing the mouthpiece. This chemlight strap has a heavy gauze on one side to allow for use of a riot gas mask with the strap removed. This chemlight strap is used by military personnel and also by civilians during search and rescue missions. This chemlight strap was specifically designed to attach a gas mask with an o-ring requiring the o-ring to be removed in order to obtain the O-ring replacement. Package Contents: United Shield Gas Mask Strap United Shield GMStrap: Gas Mask Strap