A coupling unit for transmission of a rotary driving force, comprising: - a first coupling member having a curved first bearing surface ; - a second coupling member having a main coupling body and a curved second bearing surface engaging the first bearing surface thereby enabling rotation of the second coupling member relative to the first coupling member ; wherein: - the second bearing surface is arranged at a distance from the main coupling body and comprises at least two curved second bearing surface segments which each engage the first bearing surface ; - the second coupling member comprises at least two carrying elements , which are each provided with a respective one of the at least two second bearing surface segments , and at least two connecting elements , which each connect a respective one of the at least two carrying elements with the main coupling body ; characterized in that : - the first coupling member comprises a blocking element arranged between the first bearing surface and the main coupling body ; - at least one of the at least two connecting elements comprises an elastically deformable material in a first deformed condition providing a first biasing force urging the at least two second bearing surface segments into contact with the first bearing surface ; - the blocking element is configured to prevent passage of the at least two carrying elements along the blocking element at least in the first deformed condition of the elastically deformable material; and - the elastically deformable material is provided such that, in a second deformed condition of the elastically deformable material, the elastically deformable material provides a second biasing force larger than the first biasing force and the at least two carrying elements are able to pass along the blocking element . - a first coupling member having a curved first bearing surface ; - a second coupling member having a main coupling body and a curved second bearing surface engaging the first bearing surface thereby enabling rotation of the second coupling member relative to the first coupling member ; - the second bearing surface is arranged at a distance from the main coupling body and comprises at least two curved second bearing surface segments which each engage the first bearing surface ; - the second coupling member comprises at least two carrying elements , which are each provided with a respective one of the at least two second bearing surface segments , and at least two connecting elements , which each connect a respective one of the at least two carrying elements with the main coupling body ; - the first coupling member comprises a blocking element arranged between the first bearing surface and the main coupling body ; - at least one of the at least two connecting elements comprises an elastically deformable material in a first deformed condition providing a first biasing force urging the at least two second bearing surface segments into contact with the first bearing surface ; - the blocking element is configured to prevent passage of the at least two carrying elements along the blocking element at least in the first deformed condition of the elastically deformable material; and - the elastically deformable material is provided such that, in a second deformed condition of the elastically deformable material, the elastically deformable material provides a second biasing force larger than the first biasing force and the at least two carrying elements are able to pass along the blocking element . <EOS>