> Tom, I don't know ABOUT 3M masks but most I have used have a plastic
> snap-on piece that holds the prefilter to the cartridge. It usually is
> attached to the cartridge and must be removed to insert the filter.Some of
> the ones I have used look like the plastic lid that goes on a coffee can
> after opening. the pre-filter is for paint and dust but not necessary for
> epoxy vapor only. A nylon stocking wrapped around the pre-filter and held
> with a rubberband will work for dust till you get the right parts to hold
> the pre-filters. BTW/ the cartridges don't last forever. If you can smell
> vapors the cartridge needs replacing or the pre-filter is plugged and your
> sucking air around the face seal. I vacuum outside and wipe all internal
> surfaces,especially face seal with mild soap after each use and let
> throughly before storing in a tyvek bag.

> Larry C.

larry thanks for the tips

Tom