Trailer Tongue Locks: A-Frame vs Straight Tongue Fit
Our top picks
Proven Industries Model S175
Proven's lowest-priced coupler lock.
$120 (provenlocks.com list)
Check price at Proven ↗Proven Industries Model 2516
Custom fit wraps the coupler, little room for tools.
$250 (provenlocks.com list)
Check price at Proven ↗Master Lock 379ATPY
Low price.
About $36 (masterlock.com list)
Check price at Master Lock ↗
Comparison
| Lock | Best for | Fits | Price (approx.) | |
|---|---|---|---|---|
| Proven Industries Model S175 | Best for A-frame and straight 2 in | 2 in A-frame welded-on and straight bolt-on couplers (per maker) | $120 (provenlocks.com list) | Check price ↗ |
| Proven Industries Model 2516 | Best for 2-5/16 in | Most 2-5/16 in trigger- and thumb-latch couplers | $250 (provenlocks.com list) | Check price ↗ |
| Master Lock 379ATPY | Best budget universal | 1-7/8 in, 2 in and most 2-5/16 in couplers | About $36 (masterlock.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
Proven Industries Model S175
Who it is for: 2 in trailers wanting Proven quality on a smaller budget.
- Proven's lowest-priced coupler lock
- Fits A-frame and straight-tongue couplers
- Made in USA
- 2 in couplers only
- Slides over the flange rather than fully wrapping like the 2516
- Type: Coupler lock (slides over coupler flange)
- Fits: 2 in A-frame welded-on and straight bolt-on couplers (per maker)
- Build: Made in USA, Cobra tubular lock core standard, disc-detainer upgrade optional
- Keyed alike: Yes (keyed-alike option)
- Price: $120 (provenlocks.com list)
Proven calls it its most affordable coupler lock.
Check price at Proven ↗Proven Industries Model 2516
Who it is for: Owners of valuable 2-5/16 in trailers stored unattended.
- Custom fit wraps the coupler, little room for tools
- 1/4 in steel, tubular key
- Keyed-alike option across the range
- Can capture most safety chain hooks
- Expensive
- Must match your exact coupler model
- Heavy
- Type: Coupler lock (custom-fit)
- Fits: Most 2-5/16 in trigger- and thumb-latch couplers
- Build: 1/4 in steel, black powder coat, puck lock, 7-pin tubular key
- Keyed alike: Yes (keyed-alike option across Proven line)
- Price: $250 (provenlocks.com list)
Can secure most 5/16 in safety chain hooks per maker; check the fit index for your coupler.
Check price at Proven ↗Master Lock 379ATPY
Who it is for: Budget buyers and people with several trailers.
- Low price
- Fits 1-7/8, 2 and most 2-5/16 in couplers
- Rekeyable commercial version
- Looser universal fit
- Lighter than custom steel locks
- Type: Universal coupler lock
- Fits: 1-7/8 in, 2 in and most 2-5/16 in couplers
- Build: Rust- and corrosion-resistant body, keyed different, rekeyable commercial version
- Keyed alike: Can be ordered keyed-alike commercially; retail is keyed different
- Price: About $36 (masterlock.com list)
Limited lifetime warranty.
Check price at Master Lock ↗
This guide covers one angle
This page focuses on fit by tongue style (A-frame vs straight). For the full comparison of every option, see our hub guide: best trailer coupler locks.
Tongue lock vs ball lock vs hitch lock
- Tongue/coupler lock: covers the coupler; protects an unhitched trailer.
- Ball lock: a type of coupler lock that plugs the socket. See ball locks.
- Hitch lock: locks the receiver pin on your vehicle. See hitch locks.
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
Proven Industries Model S175: best for a-frame and straight 2 in. 2 in trailers wanting Proven quality on a smaller budget. If budget matters more, see the other picks above.
Check price at Proven ↗FAQs
- Is a tongue lock the same as a coupler lock?
- Yes, in everyday use.
- Do I need a 2-5/16 in tongue lock?
- Only if your coupler is 2-5/16 in; check the stamp.