Ronstan Series 50 Single Loop-Top Ball Bearing Block

The Ronstan Series 50 Single Loop-Top Ball Bearing Block is a compact low-friction block for sheets, halyards, and other controls that need a simple loop-top attachment. The loop head keeps the fitting light and uncluttered while still allowing enough movement for a properly aligned rope lead. Its ball-bearing sheave is intended for lines that are adjusted often, where friction from a plain bearing would be more noticeable to the crew. The Series 50 size gives the block useful load capacity without turning it into oversized deck hardware.

Acetal or Torlon ball bearings support the sheave through a two-stage system designed to remain efficient across the working load range. A UV-stabilized Acetal sheave runs inside impact- and UV-resistant fiber-reinforced nylon cheeks. Grade 316 stainless steel is used for the load strap and head fitting, giving the primary load path good corrosion resistance. Cheek cut-outs make the bearing area easier to rinse and inspect after heavy use.

• Two-stage ball-bearing system
• Simple compact loop-top attachment
• Grade 316 stainless-steel load hardware
• Cheek cut-outs for bearing maintenance

The block accepts line up to 1/2 in, with a published maximum working load of 1,100 lb and a 3,310 lb breaking load. Ronstan lists the weight at about 3.4 oz, keeping the assembly light enough for active running rigging. Confirm that the loop-top attachment and rope lead allow the block to align without rubbing either cheek under load. For more ball-bearing blocks and sail-control components, browse more Sailing Hardware.