Choosing your blocks
A pulley redirects a rope and reduces friction. The right model depends on the rope used, the load to be handled, and where it will be attached. Here are the 5 points to check.
1. Sheave diameter
The sheave diameter is chosen based on the rope diameter and the load. 16 mm sheaves, such as the Harken 16 mm cheek-mount Air Block, are suitable for small control lines. 20 to 22 mm sheaves, such as the Ronstan 20 mm Orbit pulley or the Harken 22 mm fiddle block with becket, are mounted on dinghy control lines. Mainsheet and jib sheet systems use 29 to 57 mm sheaves, for example, the 29 mm cheek-mount Carbo pulley or the 40 mm cheek-mount Carbo pulley.
Harken 16 mm cheek-mount Air Block
2. Working load
Each pulley has a maximum working load indicated on its specifications. It must be greater than the actual tension on the rope, taking the purchase system into account. For high-stress areas (boom vang, cunningham, forestay), high-load models exist in small diameters: the 16 mm HL Air Block, the Allen 20 mm XHL and 30 mm XHL pulleys, or the Allen 20 mm high-load pulley. The "working load" filter in the collection allows you to sort pulleys by load range.
Harken 16 mm HL cheek-mount Air Block
3. Attachment type
The attachment determines the pulley's range of motion. A cheek-mount pulley is screwed onto the deck, a swivel pulley aligns with the pull, a shackle pulley is easily removed, and a recessed block integrates into a mast or boom. Examples: 16 mm swivel Air Block, 22 mm shackle Micro Block, 29 mm recessed Bullet block, Allen 20 mm stand-up pulley.
Harken 16 mm swivel Air Block
4. Number of sheaves and integrated features
Double, triple, or multi-sheave pulleys are used to build tackle systems. A becket allows you to attach the standing end of the rope, and an integrated cam cleat allows you to lock the adjustment. The triple Micro Block with cam cleat and becket, the 29 mm double Bullet block with becket, or the 40 mm Allen double swivel Dynamic pulley are designed for these uses.
Harken triple Micro Block with cam cleat and becket
5. Bearing type and friction
Ball-bearing sheaves turn freely under light loads. Plain bearing sheaves handle higher loads for the same size, such as the Allen 20 mm plain bearing single pulley. Ratchet pulleys rotate in one direction only and reduce the effort required to hold a sheet: 57 mm Carbo Ratchet pulley, 45 mm Allen automatic winch ratchet pulley. For redirects without moving parts, friction rings are a lightweight alternative: 19 mm friction ring, 25 mm, or Ronstan Shock friction pulley.
Allen 20 mm plain bearing single pulley
Find all models in our pulleys, friction rings, and sheaves collection.