If you have read some of the articles in Duckworks about making your own Blocks (see links below), and want to try it, but are uncertain about making the sheaves, this may be what you need. These durable Nylon pulleys are also useful for any application where you need a rope to go around a corner with very little friction. A masthead halyard pulley would be one example.
Each of these Nylon sheaves comes with a stainless bushing approximately 1/4" OD & 3/16"ID. The chart below represents the sheave only - without the bushing.