Coupling device between a towing vehicle, especially an agricultural tractor, and a trailer

The coupling device (5) has a coupling ball (6) located on a coupling support (1) of the towing vehicle, and a ball socket (8) on the trailer to engage on the ball from above. The ball socket consists of a cast body (9) of a ferrous material, with a casting skin on at least the inner side (16) of the socket. The hardness of the ball socket is lower by 5-12 HRC, pref. 6 HRC, than the hardened steel coupling ball.