Porous metal filters for regulator inlet nipples. The filters are manufactured out of a sintered bronze (nickel plated) Part No. F-7 is rated at 50 microns 6000 psi. Part No. F-8 is rated at 35 microns 6000 psi. To add an installed filter, add "RF" to the end of a CGA nipple part number. For example, NP-210 with filter becomes NP-210RF