If you have read some of the articles in Duckworks (see links below) about making your own Blocks, and want to try it, but are uncertain about making the sheaves, this may be what you need. These cast bronze sheaves 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. A cheek block would be another.
These are cast bronze sheaves that have not been machined and may need some filing. Needless to say, the following table is approximate.