The Series MP Medium Pressure Test Plugs are capable of safely holding more pressure than the A, X or V series test plugs. These plugs have 4 to 12 (depending on the size) hardened set screws on the periphery having a knurled tip on which when tightened against the inside diameter of the pipe will offer additional friction to hold the plug under pressure. Maximum test pressures are dependent upon the friction of the test plug rubber with the inside of the pipe.