Screw Grommets for Expanded Polypropylene (EPP) Foamed Components come in two sizes fitting Delta PT® 50 and 60 screws. The series has been developed to fasten parts to foamed components, especially those made of EPP. These friction-welding bosses are effective fastening elements for EPP foams and PP honeycomb elements. Through the friction welding process these PP screw grommets are embedded in the EPP foam and securely connect to the molten material.