Dan, I believe they are the small Holt Allen snatch blocks. Somebody told me they were too light for San Francisco. We have heavy winds once in a while in Detroit and I've never had a problem. My boat is still in the warehouse. When I take it out this week I'll check the blocks to make sure they are Holt Allen. Whatever they are the company makes two sizes. Mine are the small size. I've used them for three years with no problemos.