Interplast is one of the few European companies with vertically integrated production and it is the only company in Greece that manufactures all the system components. The company's subsidiary ELVIOM S.A. manufactures the brass inserts for combined polypropylene fittings, with the following features:

• Perimeter fitting retaining grooves, in which one side of the groove has negative declination so as to retain the PP-R material and prevent removal of the metal part from the plastic part in the presence of tensile forces.

• Cross-shaped grooves at the base of the brass insert so as to prevent torsion and consequent detachment of the metal from the plastic part.

• Use of raw material with hardness lower than 105 Brinell instead of the typical 125-130 Brinell. After processing the material gains an extra 10-15 Br. in hardness and that is why it is subjected to further annealing by remaining in 350°C for one hour in order for it to return to the initial 105 Br. hardness. In this way the possibility of cracking, particularly common in fittings with female threading, is eliminated.

• The brass parts are robust type, in accordance with the specifications and requirements of the thermal welding system.

• The PP-R material overlaps the male brass inserts on the inside. In this way the metal parts are isolated from the installation preventing the deposits of solids and consequently reduced flow. Moreover, the system is protected against electrochemical corrosion.