[rotorwrench]

In Aviation, they are referred to in multiple ways depending on the application. The U-shaped Tinnerman is the only one that uses"U" in the description. Most are referred to as clip nuts. Aerospace applications use mostly fine thread for fasteners so there should be something available up to 5/16". They are made for different panel thicknesses and different distances from the edge of the panel to the center of the fastener hole.