A gasket for use in holding side members in proper position during assembly and use is provided. The gasket may be used with frameless door rail systems such as those used to secure heavy glass doors in residential and commercial buildings. The gasket holds the door rail clamping members in proper position during insertion into the door rail system, and in proper position during the insertion of the door or panel to be held therebetween. The gasket also provides a cushioned interface and a weather seal between the clamping members and the associated door or panel and eliminates the need for bonding of the gasket to the clamping mechanism(s).