
Ronstan
Ronstan Series 55 RT Orbit Block Single Swivel Head
- Full name
- RONSTAN SERIES 55 RT ORBIT BLOCK SINGLE SWIVEL HEAD
- Mfg part #
- RF56100
- UPC
- 9316800440375
- SKU
- 55257
$93.94 $110.52
● In stock — 4 available · NJ · FL
🚚 Free shipping over $100
30-day returns. Details
✓ In stock, ready to ship from our NJ & FL warehouses
Secure checkout · prices verified at checkout
Genuine parts from authorized distributors. Questions? getboatparts@gmail.com
- 30-day returns
About this part
The Ronstan Series 55 RT Orbit Block Single Swivel Head is a genuine Ronstan part (manufacturer part # RF56100, UPC 9316800440375) in our Blocks range under Sailing. 4 are in stock, shipping from our New Jersey and Florida warehouses. Shipping weight is about 0.21 lb.
Manufacturer description
Series 55 Ratchet Orbit Block™ - Single - Swivel Head - Auto & Manual
Automatic Ratchet Block
Now you can enjoy the flexibility of setting up your ratchet blocks to suit yourself. Ronstan is the only company that offers a ratchet block with both auto and manual engagement modes. In the auto mode of the ratchet mechanism engages when load is applied, but switches off when it's released. This lets the sheet run out smoothly and freely-great for rapid easing of the sheet and for gybing asymmetric spinnakers. In manual mode, the ratchet mechanism can be switched on or off as required. This is the preferred mainsheet set-up for may top sailors. Try the block in both modes and see which you prefer - you really can't go wrong.
Awesome Ratchet Block Holding Power
Quite simply, Ronstan Ratchet Orbit Blocks™ have the highest holding power available. The sophisticated NC-machined sheave features Generation 2 of our sheave cross-hole geometry. Its holding power is up to 21:1, almost double that of our nearest competitior. The unique sheave design has 12 gripping faces which directly resist loaded line movement. Traditional designes have only 8 faces with an angled resistance to line movement. Our Generation 2 design has straight resistance faces which both distribute the load and minimise rope wear. These faces are offset from the radial line, to draw the rope down into the gripping area when under load.
Features:
Applications:
Materials:
Specifications:
Sheave Ø: 55mm(2")
Max. Rope Ø: 10mm(1/2")
M.W.L.: 250kg(550lbs)
B. L.: 650kg(1,430lbs)
Weight: 82g(2.9oz)
Automatic Ratchet Block
Now you can enjoy the flexibility of setting up your ratchet blocks to suit yourself. Ronstan is the only company that offers a ratchet block with both auto and manual engagement modes. In the auto mode of the ratchet mechanism engages when load is applied, but switches off when it's released. This lets the sheet run out smoothly and freely-great for rapid easing of the sheet and for gybing asymmetric spinnakers. In manual mode, the ratchet mechanism can be switched on or off as required. This is the preferred mainsheet set-up for may top sailors. Try the block in both modes and see which you prefer - you really can't go wrong.
Awesome Ratchet Block Holding Power
Quite simply, Ronstan Ratchet Orbit Blocks™ have the highest holding power available. The sophisticated NC-machined sheave features Generation 2 of our sheave cross-hole geometry. Its holding power is up to 21:1, almost double that of our nearest competitior. The unique sheave design has 12 gripping faces which directly resist loaded line movement. Traditional designes have only 8 faces with an angled resistance to line movement. Our Generation 2 design has straight resistance faces which both distribute the load and minimise rope wear. These faces are offset from the radial line, to draw the rope down into the gripping area when under load.
Features:
- Up to 20:1 holding power
- Smooth easing of sheets
- High performance cleating
- Swivel shackle head for unlimited block rotation.
- Stainless steel shackle head for ultimate durability and compatibility with harsh fixing points.
- Automatic & manual ratchet block
Applications:
- Mainsheet systems and spinnaker sheets on dinghies, sportsboats and small keel boats to 8M(26')
- Halyard, vang and backstay applications on boats to 8M(26')
- Spinnaker sheets on sportsboats and small keel boats (lateral lead blocks)
Materials:
- Sheave: Hard anodised Aluminium
- Ball Bearings: High compression strength carbon black Aceetal
- Frame/Cheeks: Toughened, glass fiber reinforced Nylon
- Rope Link: UV stabilized, multi-strand impregnated SK75 Dyneema®
- Head fitting: grade 316 stainless steel
Specifications:
Sheave Ø: 55mm(2")
Max. Rope Ø: 10mm(1/2")
M.W.L.: 250kg(550lbs)
B. L.: 650kg(1,430lbs)
Weight: 82g(2.9oz)
Related parts

Schaefer Marine
Schaefer Series 5 Flat Base Single Cheek Block- Alum Cheek
Part # 504-11
$100.60In stock

SeaSure
SeaSure Hatch Lock
Part # 23.35
$149.99In stock

Harken
Harken 40mm Carbo Air Block w/ Cam Cleat and Becket
Part # 2646
$131.95In stock

Harken
Harken 40mm Carbo Single Ratchet Block w/ Swivel
Part # 2610
$153.95In stock