Structures Footboard Extension Brackets Easily attach a footboard. Universal and Queen/Full/Twin Compatible. Sizes for Twin-King or Cal King. Modify existing bed frame to attach footboard. Compatible with Universal and Queen/Full/Twin bed frames. Universal footboard bracket extender for Twin–King sizes or for Cal King size. . . Easily attach a footboard Universal and Queen/Full/Twin Compatible Sizes for Twin-King or Cal King Modify existing bed frame to attach footboard Compatible with Universal and Queen/Full/Twin bed frames Universal footboard bracket extender for Twin–King sizes or for Cal King size