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Hitch Lock
A hitch lock does two jobs: it stops someone pulling out your hitch pin and walking away with your ball mount or bike rack, and it stops a parked trailer being hooked up and towed away. This guide explains the types of hitch lock, how to measure the pin size and span you need, and how to combine locks for better security.
Types of hitch lock
| Type | What it protects | Notes |
|---|---|---|
| Receiver hitch pin lock | Ball mounts, bike racks and cargo carriers in the receiver | Replaces the standard pin and clip |
| Coupler lock (ball lock) | A trailer coupler when the trailer is attached to the vehicle | Blocks the coupler latch |
| Universal trailer / coupler lock | An unhitched trailer | Fills or blocks the coupler so no ball can be inserted |
| Receiver lock for gooseneck / fifth wheel | Kingpins and gooseneck couplers | Specialised shapes |
| Wheel lock / boot | Any parked trailer | Stops the wheel turning |
| Hitch receiver plug lock | An empty receiver | Keeps dirt out and deters tampering |
Compare receiver pin locks, coupler locks and trailer wheel locks.
Pin size by receiver class
| Receiver | Typical opening | Typical pin diameter |
|---|---|---|
| Class I | 1¼ in | ½ in |
| Class II | 1¼ in | ½ in |
| Class III | 2 in | ⅝ in |
| Class IV | 2 in | ⅝ in |
| Class V (heavy duty) | 2 in or 2½ in | ⅝ in or ¾ in |
| 3 in commercial receivers | 3 in | 1 in |
These are the common sizes; check your receiver and accessories. Some locks come with a sleeve (adapter) so one lock fits both ½ in and ⅝ in holes. Browse pin locks by diameter.
Measuring the span
The usable length of a pin lock — its span — must be long enough to pass through both sides of the receiver and whatever is inserted (ball mount, bike rack shank or anti-rattle device). Standard receivers often need a span of around 2½–3½ inches for 2-inch receivers, but anti-rattle devices and some accessories need more. Measure across the outside of the receiver at the pin hole and add a little clearance.
Coupler locks
- Latch-style locks slip through the coupler latch hole when the trailer is attached, stopping the latch opening.
- Ball-style (universal) locks sit in the empty coupler of a parked trailer so it cannot be lowered onto a ball.
- Measure your coupler ball size (commonly 1⅞, 2 or 2 5/16 in) and choose a lock made for it.
- Look for hardened steel, a pick-resistant lock cylinder and a weather cover.
See coupler locks and universal trailer locks.
Keyed-alike sets
If you use several locks — receiver pin, coupler and perhaps a wheel lock — a keyed-alike set lets one key open them all. Many brands sell kits with two or three locks keyed alike, and some can be re-keyed to match. Keep a spare key somewhere other than the vehicle.
Browse keyed-alike hitch lock sets.
Weather and maintenance
- Choose locks with dust caps or rubber covers.
- Stainless or plated finishes resist rust; a rusted lock can seize.
- Spray a dry lubricant or graphite into the cylinder a few times a year.
- Don’t use grease in the keyway, which attracts dirt.
- In winter, a lock de-icer helps if a cylinder freezes.
Making a trailer harder to steal
- Park it where it is visible and lit, or in a locked yard.
- Use a coupler lock on the unhitched trailer.
- Add a wheel lock or boot.
- Turn the trailer so the coupler faces a wall or obstacle.
- Record the VIN and take photos; consider a hidden tracker for valuable trailers.
- Remove a wheel for long-term storage if practical.
No lock is theft-proof; layering several visible deterrents makes a thief more likely to move on. See wheel locks.
Who this guide is for
Owners of trailers, caravans, boats on trailers and vehicles with bike racks or cargo carriers. We explain types, sizes and security practices; we do not run hands-on tests. Check each lock’s pin diameter, span, materials and compatibility on the merchant page.
Frequently asked questions
What size hitch pin lock do I need?
Usually ½ in for 1¼ in receivers and ⅝ in for 2 in receivers; check your receiver.
What is the span of a hitch lock?
The usable length of the pin between the head and the lock; it must pass through the receiver and the inserted accessory.
What is the difference between a coupler lock and a hitch pin lock?
A pin lock secures accessories in the receiver; a coupler lock secures the trailer coupler.
Can I get locks that use the same key?
Yes, many brands sell keyed-alike sets.
How do I stop my hitch lock rusting?
Keep the cap on and use dry lubricant or graphite a few times a year.
Does this site test hitch locks?
No. We explain types and specifications and do not run hands-on tests. Check each merchant’s page for current details.