Extension ring. 1/2 in. Made of metal. Octogonal junction boxes with BX clamps or with conduit KOs are mainly used for commercial lighting and junction applications using BX, EMT or rigid conduit. Conduit KO's boxes require the use of proper connectors. Extensions are used to add extra capacity to a box or when installing new wall surfaces. For octogonal box. Also offered with 4 in. x 4 in. x 1/2 in. screws.