Larger sails often come with these. While not strictly needed, I find this reduces the friction a bit
- The long 1/4-inch shackle provides space for the webbing that a bullet block would not. Stronger too. The shackle must be just the right width (1/2-inch); some are wider and the rope could jump.
- The webbing bit is an 8-inch climbing sling from REI, something I had retired from climbing use. You need this length to get the block clear of the luff.
- The blocks are self-contained Harken Bullet sheaves, left over from a prior project that didn't work so well. Always recycling.
- I did drill out the inside of the blocks just a touch. About 1/64-inch.
Note 4-24-2014: After 2 years of use, the block on the 2nd reef was crushed. Too much load. I replaced it with a solid sheave turned from HDPE. No further problems.