Best Boat Trailer Locks
Our top picks
Best budget (surge-brake fit)
Master Lock 389DAT
Low price.
About $36 (masterlock.com list)
Check price at Master Lock ↗Best universal
Trimax UMAX100
Hardened steel with nylon housing.
About $130 (trimaxlocks.com list)
Check price at Trimax ↗Best custom-fit 2 in
Proven Industries Model 2178
Custom fit for 2 in couplers.
Check current price
Check price at Proven ↗Quick answer: Most boat trailers use a 2 in coupler, often with a surge brake. The Master Lock 389DAT (about $36) lists surge-brake and rolled-lip fit; for more protection choose a full-coverage Trimax UMAX100 or a custom-fit Proven 2178 (2 in) or AMPLock boat coupler lock. Add a wheel lock for winter storage.
Comparison
| Lock | Best for | Fits | Price (approx.) | |
|---|---|---|---|---|
| Master Lock 389DAT | Best budget (surge-brake fit) | Most 1-7/8 in, 2 in and 2-5/16 in couplers incl. surge-brake, rolled-lip, UFP | About $36 (masterlock.com list) | Check price ↗ |
| Trimax UMAX100 | Best universal | Most 1-7/8 in, 2 in and 2-5/16 in couplers | About $130 (trimaxlocks.com list) | Check price ↗ |
| Proven Industries Model 2178 | Best custom-fit 2 in | Most 2 in couplers | Check current price | Check price ↗ |
| AMPLock (coupler, gooseneck, kingpin, hitch, latch pin, door locks) | Best custom-fit alternative | Coupler (boat, RV, cargo), gooseneck (Bulldog, Atwood), kingpin, hitch 1-1/4 to 3 in, latch pin, barn/roll-up door | Check current price | Check price ↗ |
| Trimax TCL65 | Best for winter storage | Tires roughly 6 to 10.5 in wide span, 7.25 in reach | About $163 (trimaxlocks.com list) | Check price ↗ |
How we chose: picks are based on published specifications, materials, fit charts, manufacturer information and patterns in owner reports. We have not lab-tested these locks. Prices are approximate list prices seen on maker sites in October 2026 and change often.
Our picks in detail
Best budget (surge-brake fit)
Master Lock 389DAT
Who it is for: Boat and utility trailers on a budget.
Pros
- Low price
- Wide fit incl. surge-brake couplers
- Bright red is a visible deterrent
Cons
- Cannot be keyed alike
- Universal fit leaves room to pry
- Type: Universal coupler (ball) lock
- Fits: Most 1-7/8 in, 2 in and 2-5/16 in couplers incl. surge-brake, rolled-lip, UFP
- Build: Red powder-coated steel, wafer tumbler, keyway cover
- Keyed alike: No (cannot be keyed alike)
- Price: About $36 (masterlock.com list)
Bright red as a visual deterrent.
Check price at Master Lock ↗Best universal
Trimax UMAX100
Who it is for: Owners wanting more security than budget locks without custom-fit prices.
Pros
- Hardened steel with nylon housing
- Fits 1-7/8, 2 and 2-5/16 in
- Keys alike with other Trimax locks
Cons
- Universal fit, not glove-tight
- Bulkier than budget locks
- Type: Universal coupler lock
- Fits: Most 1-7/8 in, 2 in and 2-5/16 in couplers
- Build: Solid hardened steel, ballistic nylon housing, 9/16 in shackle
- Keyed alike: Keys alike to other Trimax locks (per catalog)
- Price: About $130 (trimaxlocks.com list)
Best custom-fit 2 in
Proven Industries Model 2178
Who it is for: Boat and utility trailers with 2 in couplers wanting top security.
Pros
- Custom fit for 2 in couplers
- 1/4 in steel
- Keyed-alike option
Cons
- Price not confirmed on our check
- Fit is coupler-specific
- Type: Coupler lock (custom-fit)
- Fits: Most 2 in couplers
- Build: 1/4 in steel, black powder coat, puck lock
- Keyed alike: Yes (keyed-alike option)
- Price: Check current price
2 in version of Proven's coupler lock (spec per dealer listing at nctrailers.com).
Check price at Proven ↗Best custom-fit alternative
AMPLock (coupler, gooseneck, kingpin, hitch, latch pin, door locks)
Who it is for: Owners who want custom-fit security and a fit-finder.
Pros
- Custom-fit range for many coupler types
- 5-year warranty with registration
- Fit quiz on maker site
Cons
- Prices not confirmed on our check
- Heavy
- Type: Custom-fit lock range
- Fits: Coupler (boat, RV, cargo), gooseneck (Bulldog, Atwood), kingpin, hitch 1-1/4 to 3 in, latch pin, barn/roll-up door
- Build: Heavy-duty steel, custom-fit; fit quiz on site
- Keyed alike: Check per model
- Price: Check current price
5-year warranty with registration (per maker).
Check price at AMPLock ↗Best for winter storage
Trimax TCL65
Who it is for: Storage of boat, utility and camper trailers.
Pros
- Doubles as a wheel chock
- Adjustable span 6 to 10.5 in
- Rubber-coated arms protect rims
Cons
- Must fit your tire width and fender clearance
- Slower to fit than a coupler lock
- Type: Wheel chock lock
- Fits: Tires roughly 6 to 10.5 in wide span, 7.25 in reach
- Build: Heavy-gauge powder-coated steel, rubber-coated arms, built-in chock
- Keyed alike: -
- Price: About $163 (trimaxlocks.com list)
Salt water and corrosion
Boat trailers get dunked. Pick powder-coated or stainless parts, keep the keyway cover closed, rinse with fresh water after launching and lubricate the cylinder with a dry lock lubricant a few times a season.
At the ramp and in storage
- While the boat is on the water, lock the empty trailer to your vehicle with a locking hitch pin and latch lock.
- In storage, use a coupler lock plus a wheel lock.
- Consider a GPS tracker hidden in the boat or trailer frame.
How to choose
- Ball size: read the size stamped on your coupler (1-7/8 in, 2 in or 2-5/16 in). Custom-fit locks are sold per size; universal locks cover all three but fit looser.
- Coupler type: trigger latch, thumb latch, lever/latch style (Atwood-type), surge-brake (common on boat trailers) or cast-steel. Custom-fit makers publish fit charts; check yours before buying.
- Material and coverage: thick steel that wraps the whole coupler leaves less room for pry bars and cutters than a small ball plug with an exposed shackle.
- Lock cylinder: tubular and disc cylinders resist picking better than basic wafer locks. Look for a keyway cover so dirt and road salt stay out.
- Keyed alike: if you also lock the hitch pin, spare tire or doors, a keyed-alike set means one key for everything.
- Weather: powder coat, stainless pins and sealed keyholes matter if the trailer sits outside or near salt water.
Our pick
Master Lock 389DAT: best budget (surge-brake fit). Boat and utility trailers on a budget. If budget matters more, see the other picks above.
Check price at Master Lock ↗FAQs
- What size coupler is on a boat trailer?
- Many use 2 in; larger boats may use 2-5/16 in. Check the stamp on the coupler.
- Do coupler locks fit surge brake couplers?
- Some do; Master Lock lists surge-brake fit for the 389DAT. Check before buying custom-fit models.