A conduit system for supporting and clamping a bank of conduits of different diameters in a substantially parallel and spaced apart relationship which requires a minimum number of parts and which can be assembled simply and rapidly. The basic structure is comprised of a plurality of vertically and horizontally interlocking modular units, each consisting of a frame member having at least one side thereof including an arcuate surface corresponding to the outside diameter of a first conduit. The conduit is supported on the arcuate surface of one frame member and clamped thereon by a second, superimposed, interlocking frame member. A unitary generally U-shaped adapter is employed to support a smaller diameter conduit within the system. One end of the adapter includes a snap-on clip to facilitate attachment to an arcuate surface of a frame member and the opposite end comprises a pair of opposed resilient arms for receiving and holding the smaller conduit in a fixed relationship to the arcuate surface.