3M 501 PRE FILTER RETAINERS PK2 Allows a 3M™ Particulate Filter 5000 Series to be combined with a 3M™ Gas and Vapour Filter 6000 Series to offer protection against airborne particles Suitable for use with all 3M half and full face masks Can be used with 3M™ Filters 5000 Series to add particulate protection to the gas and vapour filters Easy to snap into position over the filter 3M™ Retainer 501 allows a 3M™ Particulate Filter 5000 Series to be combined with a 3M™ Gas and Vapour Filter 6000 Series to offer protection against airborne particles.