21,718. Brown, R. Sept. 26. Pulley-blocks.-In pulley-blocks used for raising and lowering boats and for other purposes, rows of rollers are used instead of the ordinary sheaves. As shown in Fig. 1, the rollers bare arranged in concentric semicircles between the frame-plates a. The pins c on which the rollers are mounted may be secured to the plates a, or may be free to turn therein. In a modification, shown in Fig. 6, the rollers b are placed one behind the other, two rollers being fitted on each pin c. In another modification, the rollers are arranged in horizontal rows instead of in semicircular formation.
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