Wolf Pumps' sight check nipple is made of extra-thick clear acrylic sight glass for strength. Features include grade 5 plated bolts, nuts and washer; close-grained, cast-iron NPT male connection ends; bronze poppet machined for a proper fit; a rubber seal for positive lock against backflow; stainless spring; and a gasket on end of acrylic to help prevent leakage. A steel cover is designed to protect against weather and physical damage, and the product is available in 3- and 4-inch male NPT connections.