Systems for supporting pipes and other loads from elongated struts and channels. Clamps, connectors, and other fittings (90) for attaching the supported load to the channel (62) fit into cooperating notches (78) formed in flanges (72, 74) spaced inwardly from the side walls (64, 68) of the channel. The interfitting relationship provides a positive connection between the fitting (90) and the channel (62) keeping even heavy loads and loads subjected to vibration hammering, or the like and supported from the channel slipping, even if the supporting channel is vertically oriented and the load is therefore the most susceptible to slippage.