More details. I was back in the shop today, and as it happens, I was getting out a number of pieces of pine, and it occurred to me I could take some pictures of the stop block on my sled while I used it today.
This is the saw and the sled I use, the stop block has a partial saw kerf on the bottom edge. The kerf on the stop block is chopping off the point of the blue arrow. (I write notes to myself everywhere.)
This is me holding the block on the sled, to show where the kerf goes. To use it, I'd just drop it flat. I was holding it up to show the kerf.
The block ready to cut.
The block has a slight angle on the surface the material hits, the short point is to the sled and the material hits the long point. The angle is on the vertical edge closest to the kerf in the sled.
The partial kerf on the bottom of the stop block is for sawdust. As each piece of material is pushed up against it, any sawdust sitting on the sled from the last cut is pushed into the kerf, and the curve of the kerf then eventually pushes it out of the way. The purpose of this is so that sawdust doesn't build up against the stop block, which allows the material to be pushed completely against the block itself each time.
It's simple. It's scrap. It's cheap. It's fast. If you mess up and slice your stop block to shreds, grab another piece of scrap and go back to work.