Abstract: A knife block for mounting two knives in a staggered knife tufting machine and another knife block for mounting two knives in an aligned knife tufting machine have a pair of flanges connected together by a central web. A knife receiving channel is formed on each side of the web, each channel including a pair of aligned facing grooves in the flanges. A pair of circular bores extend transversely through one of the flanges and opens into the grooves in that flange. A cylindrical clamping member of slightly smaller diameter than the bores is positioned in each bore and forced by a screw threaded into the flange toward the other flange. The screw is received within a radial recess in the clamping member which is larger in diameter than the screw to allow for manufacturing tolerances so that the clamping member can clamp a knife in each channel. In the staggered knife block the clamping member has two different diameters.