The UltraPly TPO InvisiWeld & InvisiWeld-S Plates are designed to secure roof insulation and Elevate UltraPly TPO roof membrane. The plates are 3" (76 mm) (nominal) round, and made with specially formulated, coated galvanized steel. The plates are installed with Elevate All Purpose, Heavy Duty, Concrete Drive or Purlin fasteners on steel, wood or structural concrete roof decks.