The Monoflex 678XA monitoring well plugs from Campbell Manufacturing Inc. are designed to provide a watertight, tamper-proof seal at the top of a monitoring or observation well. The plug slips into the open end of the well pipe; turning the lockable brass wing bolt expands the Buna-N seal and secures the plug. The glass-filled, nylon top sheds water and features a molded-in “test well — no fill” warning. Available in 2-, 4- and 6-inch sizes, these well plugs fit Schedule 40 PVC, .188-inch wall steel and Schedule 5 or 10 stainless steel monitoring pipe. Campbell Manufacturing Inc.