Milling tool body and an assembly

A milling tool body being rotatable around a central rotation axis, the milling tool body comprising:

• a front end surface;
• a rear end surface;
• an envelope surface surrounding the central rotation axis and extending between the rear end surface and the front end surface;
• a plurality of insert pockets formed in a transition between the envelope surface and the front end surface;
• a first central through-hole having a constant diameter extending between the rear end surface and the front end surface;
• a locking disc having a second central through-hole;
• and
• a fastening device arranged to extend through the second central through-hole of the locking disc, wherein the locking disc is arranged to press against the front end surface of the milling tool body when mounting the milling tool body to an adaptor by the fastening device, the fastening device being mountable to an end of the adaptor insertable into the first central through-hole of the milling tool body.