Abstract: A screw clamp for clamping a flexible tubing includes a handle having a screw housing attached to one end. The housing has apertures in opposed side walls through which the flexible tubing can be passed, a base for supporting one surface of the tubing, and a bore above the base having internal screw threads in the wall thereof. A thumbscrew is threaded in the bore and defines a variable opening with the base. The handle is adapted to be gripped by the middle, ring and small fingers of the hand so that the thumbscrew can be rotated with the thumb and forefinger of the same hand to clamp the flexible tube against the base of the screw housing.