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How Hitch Couplers Work

Choosing Hitch Couplers

Heavy towing equipment
Robert Robinson/iStockphoto
Heavy-duty hitch hardware is required for extremely heavy trailers.

The basic duty of a trailer hitch coupler is to secure the trailer to the ball mount, which is located on the hitch receiver. All couplers have a mechanism that locks the tongue to the ball mount. Towing a trailer can be a balancing act that requires a bit of driver skill and proper planning. Anytime you choose a hitch and coupler, you must first determine several factors. First, weigh the trailer to measure the gross trailer weight (GTW) and the tongue weight (TW). These two measurements will allow you to determine the best option for safe towing. To measure TW, place a bathroom scale on top of a cinder block and drop the tongue level as if you were hitching the trailer. You may need to adjust the height of the scale to make sure you keep the trailer level. If the tongue weight of your trailer is heavier than 250 pounds, you may need to use a larger scale. When measuring GTW, you want to make sure you are weighing a fully loaded trailer. You can usually find these types of scales at truck rental yards and recycling centers.

The second factor to consider is towing capacity. This refers to the amount of total weight a vehicle can tow in conventional mode whereas weight distributing refers to a trailer equipped with spring bars that distribute the weight between the front and rear axles. Finally, make sure you understand your vehicle's maximum towing capacity.

Trailer hitches, ball mounts and couplers are classified by the amount of weight they can withstand. Before we learn about your hitch coupler options, let's take a brief look at class ratings and the weight range each covers:

Hitch Class Max TW (WC) Max GTW (WC) Max TW (WD) Max GTW (WD)
I up to 200 lbs. up to 2,000 lbs. N/A N/A
II up to 300 lbs. up to 3,500 lbs. N/A N/A
III up to 600 lbs. up to 6,000 lbs. up to 1,000 lbs. up to 10,000 lbs.
IV up to 1,000 lbs. up to 10,000 lbs. up to 1,400 lbs. up to 14,000 lbs.
V up to 1,200 lbs. up to 12,000 lbs. up to 1,700 lbs. up to 17,000 lbs.


Once you have determined the tongue weight and gross trailer weight and have looked up the towing capacity of your vehicle, it's time to choose a hitch coupler. Let's take a brief look at the different types and their characteristics below:

  • Straight tongue/channel style -- coupler with a square tubular mounting sleeve or tongue that can be bolted or mounted to trailer
  • Fold-away straight tongue -- similar to a channel style only they can be moved 180 degrees for stowing away
  • A-frame -- solid stamped steel couplers that are used for heavier loads
  • Flat mount couplers -- instead of a channel, the mounting face is flat and can be bolted or welded
  • Lunette ring -- steel ring that is used in conjunction with a pintle eye hitch, which is used for heavy trailers
  • Gooseneck -- long tubular shaft coupler that is used in conjunction with a gooseneck hitch, which is commonly used on heavy trailers such as horse trailers

Channel or A-frame couplers are the most common choice for class I, II and III trailers. Channel couplers slip over a square steel tube or tongue while an A-frame coupler mounts on an angled A-frame tongue. The A-frame couplers have a wider base, so they can bear more weight. When choosing a channel coupler, make sure to match it with the same tongue size.

Lunette ring couplers are used with pintle eye hitches and can be fixed or adjustable. A fixed Lunette ring coupler, commonly known as a four-hole base Lunette ring coupler, is attached to the trailer using four bolts. An adjustable Lunette ring coupler slides up and down inside a channel bracket and can be adjusted for different heights depending on the height of the trailer mount.

Now that you know what you're looking for, let's consider price and installation in the next section. You'll be towing in no time.