This is very handy for cutting a number of crosscuts the same length, using the rip fence safely. The block prevents kickback.  It is utterly indispensable for cutting pieces for segmented turning where you cut hundreds of little pieces.  The jig is made of a piece of hardwood plus two clamps (from Rockler) which fit into two holes drilled in the block.  If you mill the wood block exactly 1 inch thick, then your rip fence gauge reads accurately; just subtract an inch, and, as set up in the photograph, you will cut a piece 1-1/8 inches long. You wanted simple; this is it. . . Of course you can do this with any wood scrap and a small clamp. But then you don’t know the exact width of the scrap, and the clamp is always in the way. . .