The Sta-Lok Supajust "Eye & Blank" turnbuckle is a marine-grade stainless steel standing rigging tensioner whose eye end connects to a chainplate via a shackle or toggle, while the blank end accepts a Sta-Lok swaged or swageless wire terminal. Its Supajust barrel lets you tension a shroud or stay in place, without removing the fitting from the wire.
Standing rigging shackles and turnbuckle hardware are among the most safety-critical components on any sailboat. When a shroud or stay loses tension — or a fitting fails — the mast can go with it, so correct sizing, thread matching, and secure mousing matter more here than almost anywhere else on deck.
Sta-Lok Supajust Eye & Blank at a glance
| Feature | Detail |
|---|---|
| Type | Supajust turnbuckle, Eye & Blank configuration |
| Material | High-grade (316) stainless steel |
| Eye end | Fixed loop — connects to chainplate via shackle, clevis pin, or toggle |
| Blank end | Accepts a Sta-Lok swaged or swageless wire terminal threaded into the barrel |
| Adjustment | In-situ tensioning — barrel rotates without removing the terminal from the wire |
| Typical use | Cap shrouds, forestays, backstays on mid-to-large cruising and racing yachts |
What is a shackle, and how does it relate to standing rigging?
A shackle is a U-shaped metal fastener closed by a pin, used throughout marine rigging to connect lines, fittings, and structural hardware. In standing rigging, shackles attach turnbuckle eye terminals to chainplates, deck plates, or toggle forks. They are load-bearing connectors that must be rated, inspected, and properly moused (secured against unscrewing under vibration) — a single failed shackle in a shroud circuit can lead to dismasting.
A bow shackle (also called an anchor shackle) has a rounded, omega-shaped bow for multidirectional loading, while a D-shackle — a clevis-style shackle — has a narrower profile suited to in-line loads. The eye terminal on the Sta-Lok Supajust mates directly with a D-shackle or toggle, keeping the load axis aligned through the turnbuckle body.
What is the Sta-Lok Supajust turnbuckle used for?
The Supajust turnbuckle is the tensioning element in a shroud or stay circuit. The eye end connects to the chainplate via a shackle or toggle; the blank end accepts a Sta-Lok or compatible wire terminal. Rotating the barrel threads the two ends together, increasing tension in the stay. Crucially, the Supajust design lets you perform this rotation while the terminal stays attached to the wire — a real advantage over conventional open-body turnbuckles that must be removed for adjustment.
The "Eye & Blank" designation describes the two ends. The eye end is a fixed loop that accepts a shackle, clevis pin, or toggle. The blank end has no preformed terminal; instead it accepts a Sta-Lok swaged or swageless wire fitting that threads directly into the barrel. This is common on cap shrouds, forestays, and backstays where the lower end needs a shackle connection and the upper end terminates directly onto the wire.
How do I choose the right Supajust turnbuckle size?
Selecting the correct Sta-Lok turnbuckle depends on wire diameter, breaking-load requirements, and the thread pitch of your existing or planned terminals. Matching the thread size across the entire rigging circuit — turnbuckle barrel, wire terminal, and toggle — is critical. Mismatched threads cannot be safely forced together and will strip under load.
The shank diameter of any shackle used with the eye terminal should be sized to match the eye bore: oversized shanks will not close properly, and undersized shanks introduce point loading. When in doubt, cross-reference the thread specification against your existing Sta-Lok terminal part numbers before ordering, or ask a rigger to confirm the load rating for your boat.
How do I install and tension the Supajust Eye & Blank?
- Inspect the eye bore: confirm it is free of corrosion or deformation before connecting any shackle.
- Select the correct shackle: use a marine-grade 316 stainless D-shackle or bow shackle rated above the shroud's breaking load, with a shank that fits cleanly through the eye without excessive play.
- Thread the shackle pin fully: engage all threads before loading — hand-tight plus one full turn, then mouse with stainless seizing wire through the pin hole. Do not use pliers.
- Attach the blank-end terminal: thread your Sta-Lok wire terminal into the blank barrel end following Sta-Lok's published assembly values — do not estimate.
- Tension the stay: rotate the Supajust barrel to tension; because it rotates without disassembly, intermediate tensioning during tuning is straightforward.
- Lock the barrel: use the Sta-Lok locking nut or seizing wire across the barrel slots per the manufacturer's spec to prevent unthreading under vibration.
Some sailors prefer a clevis pin and toggle at the chainplate instead of a shackle. A clevis gives a lower-profile, in-line load path and is less prone to toggling fatigue under cyclic loading. The eye terminal is compatible with both — confirm bore diameter against your toggle or chainplate pin size before final installation. After final adjustment, verify shroud and forestay tension with a calibrated rig tension gauge.
Frequently asked questions
What is a shackle in sailing rigging?
It is a U-shaped metal connector closed by a threaded or captive pin, used to link rigging components securely. In standing rigging, shackles connect a turnbuckle eye terminal to a chainplate or deck fitting and must be rated above the shroud's breaking load and moused against vibration.
What does the "Eye & Blank" configuration mean?
One end is a fixed eye that connects to a chainplate via a shackle, clevis pin, or toggle; the opposite end is blank, accepting a Sta-Lok swaged or swageless wire terminal threaded into the barrel. This gives riggers flexibility when terminating standing-rigging wire.
How do I choose the right turnbuckle size?
Match the thread size and wire diameter across the whole circuit — turnbuckle, wire terminal, and toggle must all agree. Verify against Sta-Lok's sizing charts and your existing terminal part numbers before ordering, and confirm the load rating with a rigger if in doubt.
How do I tension a Supajust turnbuckle when tuning?
Rotate the Supajust barrel to add tension — it adjusts in place without removing the terminal from the wire. Lock the barrel with the locking nut or seizing wire, then confirm shroud and forestay tension with a calibrated rig tension gauge.
Is the Sta-Lok Supajust suitable for offshore sailing?
Yes. Sta-Lok is recognized for offshore-grade standing rigging hardware, and the Supajust's in-situ adjustment reduces the number of disassembly cycles — each of which is a potential point of thread damage or human error — making it well suited to bluewater use.
Should I use a shackle or a clevis at the eye terminal?
Both work. A shackle is quick to connect and remove; a clevis pin and toggle give a lower-profile, in-line load path with less toggling fatigue. Confirm the eye bore diameter matches your shackle shank or clevis pin before final installation.
Shop all Sta-Lok Turnbuckles →