The 57 mm Carbo Fiddle Block is a great, light weight, high load, block that you can use to add purchase. On the Flying Scot we use it for the 3 to 1 mainsheet at the end of the boom.  This is the standard rigging for the new daysailing Flying Scots.  The 3 to 1 mainsheet is linked below.

Low-friction Carbo Air blocks are lightweight, strong, reliable—and affordable.  These small, compact blocks have very high working loads for safe, easy trimming.