A tow hitch (or tow bar or trailer hitch in North America) is a device attached to the chassis of a vehicle for towing, or a towbar to an aircraft nose gear. It can take the form of a tow ball to allow swiveling and articulation of a trailer, or a tow pin, or a tow hook with a trailer loop, often used for large or agricultural vehicles where slack in the pivot pin allows similar movements. Another category is the towing pintle used on military vehicles worldwide.
To tow safely, the correct combination of vehicle and trailer must be combined with correct loading horizontally and vertically on the tow ball. Advice should be heeded (see references) to avoid problems.
Regional variations
North America
Trailer hitches for conventional passenger cars, light-duty commercial vehicles, light trucks, and multipurpose passenger vehicles come in two main OEM or aftermarket types: receiver and bumper/fixed-drawbar.
Receiver-type hitches consist of a portion with a rearward-facing opening that accepts removable aftermarket hitch-mounted accessories: trailer hitch ball mounts, hitch bike racks, cargo carriers, etc.
Bumper/fixed-drawbar type hitches typically are built as one piece, have an integrated hole (sometimes more than one hole on pickup trucks) for the trailer ball mount, and are generally not compatible with aftermarket hitch-mounted accessories.
Outside North America, the vehicle mounting for the tow ball is called the tow bracket. The mounting points for all recent passenger vehicles are defined by the vehicle manufacturer and the tow-bracket manufacturer must use these mount points and prove the efficacy of their bracket for each vehicle by a full rig-based fatigue test.
Ball mounts
The trailer hitch ball attaches to a ball mount; with a diameter typically larger than the ball bolt/shank diameter. The ball mount must match the SAE hitch class. The ballmount for a receiver-type hitch is a square bar that fits into a receiver attached to the vehicle. Removable ball mounts are offered with a varying rise or drop to accommodate variations in the height of the vehicle and trailer to provide for level towing.
Load classes
A trailer hitch typically bolts to the chassis of the vehicle. In North America, there are a few common trailer hitch classes (I, II, III, and IV) that are defined by the Society of Automotive Engineers (SAE). Class I – up to – light loads Class II – up to – light loads Class III – up to – larger loads (campers, boats, etc.) Class IV – up to – larger loads (campers, boats, etc.) Some manufacturers market Class V hitches, but there was no such standard listed in the 2014 version of SAE J684. "Class V" – up to – larger loads (construction equipment, etc.)
Receiver tube sizes
A receiver hitch can accommodate a variety of different tow hitches when the tow hook/ball may be attached via a receiver tube attached to the tow vehicle. Trailer hitch receiver tubes may be bolted, welded, or integral to the vehicle chassis, and come in various sizes depending on the load they are designed to carry and the country of operation. The US standards are: Class I & II - light or medium duty receiver tube Class III & IV - heavy duty receiver tube Class V - receiver tube
Ball sizes
Trailer hitch balls come in various sizes depending on the load they carry and the country of operation, with removable types consisting of a bolt/shank to attach to the ball mount. The trailer tongue (North America) or coupling (outside North America) slips over a trailer hitch ball attached to a receiver hitch mount or integral with the hitch.
A larger, heavy-duty gooseneck ball size: is typically used for towing greater than , and this towing capacity falls outside of the scope of SAE J684 trailer hitch classes.
Truck variants
Weight ratings for both bumper-mounted and frame-mounted receiver hitches can be found on the bumper of pickup trucks (for bumper-mounted tow balls) and on the receiver hitch (for frame-mounted receiver hitches).
For flat deck and pickup trucks towing trailers there are fifth wheel and gooseneck hitches. These are used for agriculture, industry, and large recreational trailers.