2.1 Properties of metal inserts

The diamond knurling, of a shape, pitch and depth suited to the stress to be applied, is normally adopted, aiming at ensuring the most effective anchoring of the metal inserts to the plastic material and the best mechanical operation of the element. This type of knurling ensures both axial anchoring (that contrasts axial tensile stress) and radial anchoring (to avoid rotation during the transmission of torque).

For threaded studs, instead of using a common screw available on the market, they use specially shaped threaded insert which protrudes a few tenths of mm from the plastic body so as to form a metal face on the screwing plane, thus freeing the plastic material of all stresses.