Abstract: In a power-and-free conveyor system an anti-backup devise for attachment at a work station comprising a block, and a stop and a cam mounted on the block and a spring for applying force to the cam to frictionally engage a wheel of a trolley on the power-and-tree system.

Abstract: A guide apparatus for cutting roofing shingles includes a rigid base plate, substantially rectangular in shape, having a first end wall spaced from a second end wall; a first side wall spaced from a second side wall; a cutting guide pivotally supported on the base plate along the first side wall; and upright guide surfaces mounted for sliding movement on the base plate adjacent to the second side wall. The cutting guide may be fixed at non-perpendicular and perpendicular angles to the long axis of the base plate. A scale having reference markings for cutting shingles at predetermined lengths is mounted along the first side wall. The scale may be utilized to determine points at which the beginning and the end of a cut can occur both easily and accurately. A modification of the invention includes an outward extension of the base plate along the first side wall, the extension having an opening within it, the combination serving as a carrying handle for the guide apparatus.