Towball
Towball, tow ball, hitch ball, 50 mm hitch ball, ISO 50 towball, EC 94/20 towball, ball coupling
A towball is the steel spherical end of a towbar onto which the coupler of a caravan or trailer drops and latches. In Europe the standard is a 50 mm ball to ISO 50 (EC 94/20); in the US three sizes — 1⅞″, 2″, and 2⁵⁄₁₆″ — are used. Ball geometry and condition directly affect towing safety.
The European 50 mm ball mates with couplers like AL-KO AKS or Westfalia. Wear is checked with a go/no-go gauge or callipers: new ball is 50 mm, the rejection limit is 49 mm. Finish is either black paint or chrome; AL-KO AKS stabilisers require a dry, matt, grease-free ball. Not to be confused with the towbar (the structural bracket and electrics), see the tow-bar entry.