This osteosynthesis device is of the type comprising: A support (2) provided with a through-orifice (3), at least one part (5) of the height of which is threaded, and an anchoring rod (4) having a threaded part (12) forming a screw, the thread (12) of said threaded part (12) being complementary to that (5) of said support orifice (3), in order to hold said rod (4) on said support (2) by screwing, said support (2) and said rod (4) furthermore including complementary bearing surfaces (6, 13). In accordance with the invention, the protruding ends of the screw threads (12) and support threads (5) are truncated in such a way that the difference Dtv between the outside diameter De of the screw and the diameter Df on the flanks is between 5 and 70% (preferably between 15 and 50% and even more preferably around 20%) of the difference Dsv between the nominal diameter Dn and the diameter Df on the flanks, and the difference Dts between the diameter Df on the flanks and the core diameter Dns is between 5 and 70% (preferably within 8 and 50% and even more preferably around 10%) of the difference Dss between the diameter Df on the flanks and the diameter Dff of the thread route.
