Tow Ball Sizes
Towing & Hitches · 6 specs
Direct Answer
Trailer Tow Balls (standardized globally under ISO 1103 for the 50.0 mm metric standard, and under SAE J684 for North American imperial sizes: 1-7/8", 2.0", 2-5/16", and 3.0") provide the spherical articulated mechanical pivot point between the towing vehicle and trailer coupler.
Source: ISO 1103:2007 (Road vehicles — Coupling balls for caravans and light trailers) / SAE J684 / UN ECE Regulation 55 · Last reviewed Aug 28, 2026
Specs
| ISO 1103 / European Standard | 50.0 mm (+0.0 / -0.4 mm) diameter spherical ball (ECE R55 standard; mandatory across Europe, UK, Australia, New Zealand) |
| 1-7/8 Inch (47.6 mm) | Light utility trailers, jet ski trailers, small rowboats (Class I hitches, rated up to 2,000–3,500 lb GTWR) |
| 2.0 Inch (50.8 mm) | The standard North American tow ball: travel trailers, midsize boats, car haulers (Class III hitches, rated up to 6,000–8,000 lb) |
| 2-5/16 Inch (58.7 mm) | Heavy travel trailers, 3-horse trailers, equipment flatbeds, commercial dump trailers (Class IV/V hitches, rated 10,000 to 20,000 lb) |
| 3.0 Inch (76.2 mm) | Severe gooseneck and heavy commercial industrial trailers (rated up to 30,000 lb+) |
| Critical Mismatch Warning | A 50.0 mm European ball is 0.8 mm smaller than a 2.0" (50.8 mm) ball; coupling an imperial 2" trailer onto a 50mm ball can pop off under road dips |
The Dangerous 50mm vs 2-Inch Incompatibility
While 50.0 mm (European) and 50.8 mm (2.0 inch American) look identical to the naked eye, clamping an American 2.0'' coupler onto an imported European 50 mm ball leaves an unsafe 0.8 mm mechanical clearance. When hitting a severe highway frost heave or bridge joint, the upward inertia of the trailer tongue can dislodge the loose coupler right off the ball.