A coupling part 10 of a device for a surgical handpiece 1 is proposed that can be introduced into a bore 2 of the handpiece 1 and engages with a form fit in the bore 2. The bore 2 has a collar 3 which at the proximal end has a taper and at the distal end has a flat turned portion 6 extending approximately perpendicularly with respect to the main axis 7 of the handpiece 1. The coupling part is secured in the handpiece 1 by a flexible securing ring 11, without a ratchet configuration being needed for this purpose.