is configured as a contact spring that is partially integrated into the body 12 and the clamping plate 14 in the area of the open space 13 to receive the profile rail a supporting piece of the potential equalization element 24 projects into the open space 13 the consequence is that when a profile rail is inserted into the open space 13 the profile rail strikes the supporting piece 28 and pushes the contact tip 26 which is housed in the clamping blade 14 to prevent contact through a surface 25 of the clamping blade 14 facing away from the open space 13 out of the clamping blade 14 the contact tip 26 makes electrical contact for potential equalization with an appliance or component that is to be attached to the profile rail using the fastening system provision can also be made for the force necessary to push the contact tip 26 out of the clamping blade 14 to be generated only at the time of bolting together so that the electrical contact for potential equalization is completed only the time of bolting together in addition the clamping blade 14 has an additional contact tip 27 at the opposite end from contact tip 26 that projects out of the body 12 into the open space on the side of the body 12 facing the open space 13 so that when a profile rail is pushed into the open space 13 or at the time of bolting together.