A cutting tool holder of the kind in which the fastening screw (securing member) remains engaged with the tool holder seat during mounting/dismounting of the cutting insert. The seat is further formed with a support surface configured for engaging and providing support to the head portion of the securing member at least in the securing position.

An axially elongate dental machining portion includes a machining region machinable by a dental machining device, and a fixing region for fixing the axially elongate dental machining portion to a holder of the dental machining device. In the fixing region is a fixing projection oriented transversely relative to a longitudinal axis. In a condition of the machining portion being mounted in the holder, the fixing projection bears against a holding nose positioned in complementary relationship on the holder. The machining region has a machinable surface which has a maximum spacing relative to the longitudinal axis, measured normal to the longitudinal axis, and the fixing projection has a maximum spacing relative to the longitudinal axis, measured normal relative to the longitudinal axis, that is greater than the maximum spacing of the machinable surface relative to the longitudinal axis.