A modular cutting tool holder portion for a metal-working machine includes a first engagement face configured for clamping engagement with a corresponding second engagement face of a complementary modular cutting tool holder portion. The first engagement face includes a base surface and interlocking elements in the form of exactly four projecting protrusions or exactly four recesses. Each interlocking element includes a non-contact surface spaced from the base surface. The non-contact surface includes two opposing edges between which it extends, and two abutment surfaces each extending from a respective one of the two opposing edges to the base surface and being configured for the clamping engagement.