DUBL-CHEK HM-604 is a Level 3, Method A & C, Water Washable, Fluorescent Penetrant for inspecting castings, extrusions and similar parts. HM-604 is a versatile, general purpose penetrant for use on a variety of materials, including aluminum and magnesium. Complies with low sulfur and low halogen requirements. HM604 has been used by aerospace, airframe, turbine engine and missile manufacturers for over a decade.