Ronstan Sailing Blocks

Blocks are the heart of a running rigging system, and Ronstan builds them for everything from dinghies to offshore keelboats. This collection covers the full range of ball bearing and plain bearing blocks, single through triple, plus fiddle, ratchet, and cam variants. Choosing right comes down to your line diameter, the working load, and where the block sits in the system.

Size the sheave to your line

Start with line diameter. Each block lists a maximum line size, and the sheave diameter should be large enough that the line runs freely without pinching or excess friction. A sheave that is too small chafes the line and adds drag, so match the block to the largest line that will pass through it and leave a little room.

Ball bearing or plain bearing

Ball bearing blocks spin freely under light to moderate load, which makes them ideal for sheets and control lines that you trim constantly, like a mainsheet or spinnaker gear. Plain bearing blocks carry higher static loads with less concern for free running, which suits halyards and high-load turning points that sit under tension but move less. Match the bearing to how the block is used.

Pick the configuration

Single blocks turn a line, while double and triple blocks build purchase in a tackle. A fiddle block stacks two sheaves of different sizes for a compact multi-part system. A ratchet block holds load in one direction so you can hand-hold a sheet without it slipping, which saves your hands and a cleat. Choose the configuration that builds the purchase and control your system needs.

Attachment matters

Blocks attach by shackle, loop head, or lashing. Loop and lashing heads articulate and save weight, which racers like, while shackle heads are quick to swap. Match the attachment to your padeye or becket and the load, and add a becket where you need to dead-end a line in the tackle.

Match the load to the boat

Ronstan groups blocks into series by size and load rating. Bigger boats and higher loads need a larger series with a higher safe working load. Do not undersize a block at a high-load turning point, because a failure under load is dangerous and expensive.

Not sure which blocks your rig needs? Tell our crew your line sizes and where the blocks go, and we will match the series, bearing, sheave, and attachment so the system runs smooth and holds load.