Universal Outboard Motor Lock for 3/8-7/16in Transom Bolts 316 SS
mms-357
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Outboard Transom-Bolt Security Lock
For 9.5–11.1mm bolts with at least 12.7mm exposed thread
A 316 stainless-steel security sleeve for an already tightened outboard transom bolt. It encloses the exposed threaded end to make casual tool access more difficult.
Key Features
- For 9.5–11.1 mm (3/8–7/16 in) transom bolts
- Requires at least 12.7 mm (1/2 in) exposed thread
- A4 / 316 stainless-steel construction
- Fits after the engine mounting bolt has been torqued
- Compact theft-deterrent design
Technical Specs
| Bolt diameter | 9.5–11.1 mm (3/8–7/16 in) |
| Minimum exposed thread | 12.7 mm (1/2 in) |
| Material | A4 / 316 stainless steel |
| Application | Outboard through-bolt threaded end |
| Security type | Physical access deterrent |
| 4Boats SKU | mms-357 |
Compatibility / Fitment Guide
Measure one accessible engine mounting bolt after it is correctly torqued. The threaded section outside the nut must be within the diameter range and project at least 12.7 mm, with enough radial clearance for the lock body.
| Bolt diameter | Fits 3/8 in to 7/16 in (9.5–11.1 mm) bolt threads only. It will not fit M8, M12, 1/2 in or other out-of-range hardware. |
| Thread projection | At least 12.7 mm of usable exposed thread is required beyond the nut; excess sealant, double nuts or damaged threads can prevent seating. |
| Clearance | Confirm space around the bolt for the sleeve/key or locking operation, including near splashwell sides, steering gear and rigging. |
| Correct installation | Torque the engine mounting hardware to the engine/transom manufacturer’s specification first. The lock must never be used as the fastening nut or to set bolt torque. |
| Not suitable for | Clamp-screw-only portable outboards, recessed bolt ends the body cannot reach, or bolts outside the specified diameter range. |
Part Number Cross Reference
| Bolt-size reference | 3/8–7/16 in / 9.5–11.1 mm |
| Minimum projection | 1/2 in / 12.7 mm |
| 4Boats SKU | mms-357 |
No engine-model cross-reference is appropriate; compatibility is determined by the installed mounting-bolt dimensions and access.
Frequently Asked Questions
Will it fit clamp-on tender motors?
Not if the engine is secured only by hand-operated clamp screws.
Does it replace the mounting nut?
No. Tighten the correct nut first, then fit the security device over the exposed end.
Is it theft-proof?
No security device is theft-proof. Use it as one layer with identification, alarms, tracking and secure mooring where appropriate.
Will it fit a 12mm bolt?
No; 12 mm is outside the stated 9.5–11.1 mm range.
Security hardware must not interfere with steering, trim, tilt, rigging or inspection of the engine mounting bolts.
For the products under £150 the shipping is £6.99.
Free delivery for most items over £150.
