... perimeter according to the customer’s request, and not need to machine a new mold. Type 21. Pure rubber ... perimeter according to the customer’s request, and not need to machine a new mold. Type 31. Pure rubber ... perimeter according to the customer’s request, and not need to machine a new mold. Type 41. Seal ... perimeter according to the customer’s request, and not need to machine a new mold. Type 51. Pure ...