A clamp assembly releasably secures a plumbing pipe to a support. The assembly has a clamp base releasably connected to a clamping block by pawls that releasably engage a pair of ratchet arms extending from the base. Each of the base and clamping block has two inclined surfaces forming a generally V-shaped notch that opens toward the pipe. A cap is optionally placed over one or both of the V-shaped notches and is interposed between the notch and the pipe. At least one resilient leg or a flange may extend from the base opposite the ratchet arms, with the flange and/or the arms resiliently engaging opposite sides of the support to hold the clamp assembly in position.