Bolted polypropylene fittings are equipped with 316 stainless steel bolts and come standard with EPDM gaskets. Viton gaskets are available as an option for the fittings. Bolts are threaded into the back plate of the fitting so there are no welds or bolt holes that can be potential points of leakage. These fittings come with a EPDM Gasket. Available gaskets are cross-linked polyethylene, EPDM and Viton. (4" fitting comes standard with a cross-linked polyethylene gasket.)