Ronstan blocks are the pulleys that route and redirect running rigging—sheets, halyards and control lines—with the least possible friction, and choosing the right one comes down to three numbers: the load the block carries, the line diameter running through it, and the mounting it needs. Match those correctly and the block runs smoothly and lasts; get them wrong and you invite binding, wear, or failure under load.
Ronstan has been a leader in marine hardware for decades, with ranges spanning tiny dinghy blocks up to high-load offshore gear. This guide breaks down the main block types, what each is for, and how to match one to your rig.
Ronstan block types at a glance
| Block type | Bearing | Best for | Typical use |
|---|---|---|---|
| Ball bearing | Rolling ball bearings | Low friction, frequent adjustment under light-to-moderate load | Mainsheet & control-line systems |
| Plain (sheave) | Plain bushing | High static loads, strength & durability | Turning points, halyard leads |
| Ratchet | Ratchet mechanism | Holding load in one direction with less hand effort | Dinghy & small-keelboat sheets |
| Snatch | Side-opening | Dropping a line in mid-run without threading the end | Spinnaker work, temporary leads, towing |
What are Ronstan blocks and why choose them?
A block is a sheave (pulley wheel) housed in a cheek or cage, used to change the direction of a line or build a purchase system. Ronstan blocks are engineered for high load-bearing use in demanding conditions, using precision ball bearings and quality sheaves to reduce friction for smoother operation. Stainless steel and reinforced polymer resist corrosion in harsh marine environments, and the lightweight, compact construction keeps weight off the deck and rig—with options for dinghies, keelboats and offshore yachts alike.
What are the main types of Ronstan blocks?
Ball bearing blocks minimize friction for high-speed, frequently adjusted applications, running smoothly under light to moderate loads—ideal for mainsheet and control-line systems. Plain (sheave) bearing blocks are built for heavy, static loads, trading a little friction for high strength and durability, making them the right choice for high-load turning points and halyard leads.
Ratchet blocks hold load in one direction so you can grip a loaded sheet with far less hand effort—popular for mainsheets and jib sheets on dinghies and small keelboats. Snatch blocks open on the side so you can drop a line in mid-run without threading the end—handy for spinnaker work, temporary leads and towing.
How do I choose the right Ronstan block?
Match the block to four variables. First, load rating: choose a block whose working load exceeds your peak line load, with margin for shock loads. Second, line diameter: the sheave must suit your line size—too large wastes space, too small binds and wears the line. Third, mounting: decide between fixed, swivel, or snap-shackle attachment for your lead. Fourth, usage type: racing, cruising or offshore—match the bearing type (ball vs plain) to how often the block is adjusted under load.
For Ronstan's flagship high-performance range, see our deep dive on Ronstan Orbit block technology. If you are comparing brands, our Harken blocks guide covers the same selection logic.
Frequently asked questions
How do I choose the right size Ronstan block?
Start with the load the block will carry and the diameter of the line running through it. Choose a block whose working load exceeds your peak line load with margin for shock loads, and whose sheave suits your line size—too small binds and wears the line, too large wastes space and weight.
What is the difference between ball bearing and plain bearing Ronstan blocks?
Ball bearing blocks use rolling bearings for the lowest friction and are best where the line is adjusted frequently under load, such as mainsheets. Plain (sheave) bearing blocks handle high static loads with more strength and durability, making them ideal for turning points and halyard leads that are set and left.
What is a ratchet block used for?
A ratchet block holds load in one direction so you can grip a loaded sheet with much less hand effort while still easing smoothly. They are popular for mainsheets and jib sheets on dinghies and small keelboats where the crew holds the sheet by hand.
When should I use a snatch block?
Use a snatch block when you need to add a line to a lead without threading the end through—it opens on the side. They are useful for spinnaker sheets and guys, temporary leads, and towing, where you want to drop a loaded or bulky line in quickly.
Are Ronstan Orbit blocks worth it over standard blocks?
Ronstan Orbit blocks use a two-stage bearing system and fibre-reinforced sheaves for a high strength-to-weight ratio and low friction across a wide load range. For performance sailing where weight and efficiency matter, they outperform standard blocks; for light-load cruising leads, a standard block is often sufficient.