A
coupling unit (5) for connecting a breast bar (3) to an inner wall of a horse trailer or horse
transporter or for connecting the breast bar (3) to a horse harness, comprising a groove (9) in which a bolt (7) is movable upwards and downwards, wherein downward movement is restricted by a spring (6), wherein the spring (6) is pushed back by the bolt (7) when a
high weight acts downwards on the bolt (7), whereby the bolt (7) can move out of the groove (9), wherein the
coupling unit (5) has two springs arranged opposite one another in the groove (9).