Abstract: The invention contemplates a single-piece injection-molded plastic hose clamp which may be made, shipped and stored flat and yet which, in assembly to a flexible hose may be applied to squeeze and effectively shut off flow through the hose in a one-handed shut-off operation wherein the shut-off condition is releasably locked. A hinged locking member on one arm of the clamp includes a bracket which, in reaction to the squeezing action to set the clamp, operates as a bellcrank to elevate the locking member to position for automatic resiliently loaded self-latching engagement with a coacting locking member on the other arm of the clamp.