The 3M™ Head Harness FF-400-04 is a single head harness replacement for use with the 3M™ Cool Flow™ Valve for use with 3M™ Ultimate FX Full Facepiece Reusable Respirator FF-401, FF-402, FF-403.3M Head Harness FF-400-04 is to be used with compatible products. Replacement part can extend respiratory equipment service life.