To avoid an overload of a connecting element in a coupling device and a method for connecting a connection line to a pipe connection of a washing machine with an external thread.

The coupling device includes a first end 3, and a nut 2 with an internal thread arranged in the range of the first end 3. The nut 2 includes an inner ring 7, an outer ring 6, and a slide clutch 15 arranged between the inner ring 7 and the outer ring 6. The slide clutch 15 includes a locking ratchet 16 and a recessed part 17. The locking ratchet 16 is radially inclined, and a foot 22 is mounted or formed in the end of the locking ratchet 16, and engaged in the recessed part 17. This enables reliable power transmission between the recessed part 17 and the foot 22 or the locking ratchet 16. A radial protrusion 18 is mounted or formed between the locking ratchets 16, but not radially protruded as much as the locking ratchet 16.