Master Lock Trailer Coupler Lock 379ATPY Black — Universal Fit 1-7/8–2-5/16 in, Zinc Keyed

The Master Lock 379ATPY is a universal trailer coupler lock that blocks unauthorized hitching by fitting the most common coupler sizes and providing keyed, corrosion-resistant protection.

Keep your trailer, camper, boat, or utility equipment from being hitched without permission with a compact, visible towing security device. The 379ATPY is made to fit 1-7/8 in., 2 in., and most 2-5/16 in. trailer couplers, uses a keyed locking mechanism designed to resist tampering, and features zinc construction for weather resistance. It ships with two keys so you can keep a spare where you need it.

How does this lock prevent unauthorized coupling?

The 379ATPY physically blocks the coupler latch area so another vehicle cannot connect to your trailer. Its keyed lock is engineered to resist picking and prying, creating a visible deterrent that reduces opportunistic theft.

• Solid locking bar covers latch opening to stop hitch engagement
• Keyed cylinder built to make picking difficult
• High-visibility black finish signals a secured trailer
• Includes two keys for immediate use and a spare

Will it fit my trailer's coupler sizes?

This coupler lock was designed as a universal option for the most frequently used couplers. It fits 1-7/8 in. (48 mm), 2 in. (51 mm), and most 2-5/16 in. (59 mm) trailer couplers, covering a wide range of utility, boat, and camper trailers.

• Compatible with standard round ball couplers in listed sizes
• Works with many RVs, boat trailers, utility trailers, and campers
• Compact profile fits common latch geometries without modification
• Universal fit reduces the need for multiple locks across trailers

How durable is it for outdoor use?

The lock's zinc construction helps resist rust and corrosion from rain, road splash, and marine environments. Built for frequent outdoor exposure, it offers long-lasting performance when stored on the hitch between trips or left on trailers during seasonal storage.

• Zinc body resists corrosion in wet or coastal conditions
• Solid-metal components withstand outdoor storage and handling
• Black finish reduces visible wear and integrates with tow setups
• Small size is easy to stow with other hitch accessories

What comes in the package and how do I use it?

Out of the box you get the keyed coupler lock and two keys, so you can secure the trailer immediately and keep a spare key accessible. Installation is tool-free: position the lock over the coupler latch area and turn the key to lock it in place.

• Includes the Master Lock 379ATPY coupler lock and two keys
• Tool-free installation — slide into place and turn key to secure
• Compact for easy transport with other towing accessories
• Visible deterrent for parking lots, driveways, campsites, and storage

Who this lock is for: The Master Lock 379ATPY is aimed at trailer owners who want a straightforward, visible way to help prevent unauthorized hitching—ideal for owners of boat trailers, utility trailers, campers, RVs, and jobsite trailers. If you need a compact, weather-resistant coupler lock with a universal fit and keyed security, this model provides a practical, ready-to-use option.