An article from Master Weaver No. 9 (May 1953) describing how to build and use a heck block, a sliding yarn guide for a horizontal warping mill. The block rides on a rail and is pulled by cords wound on wooden cylinders, so it travels along the mill as the frame turns, spacing the warp evenly and helping make the crosses. The text covers construction details (rail, perforated board, box, wire half-heddles, cylinders, pulleys), optional safety stops and a counter, and operating instructions. A page of line drawings (Figs. 1-6) illustrates the parts.