Half mask filters

Just a quick question for you experts ;-)
I'll be doing a load of hammerite spraying in the near future, so purchased a half mask/dual filter from cpc.co.uk (superb retailer BTW - never had a problem - and they seem to stock everything!)
http://custom1.farnell.com/cpc/product.asp?catalog%5Fname=CPC+Catalogue&category%5Fname=Tools+and+Maintenance+%2D+Health%2C+Safety+and+Hygiene+%2D+Respiratory+Protection&product%5Fid '5551
However - the universal filters (A1B1E1K1P3) are out of stock, which is annoying, but I'm unsure about what the minimum level would need to be for aerosol paint in an enclosed room, and also possibly MDF-dusty work in the future. They have A2P3, P3 and A2 filters on the site too, but I don't know if any of these are suffucient.
Also - is the fitting universal? or do I have to stick with this manufacturers' own filters?
If it is universal - can anyone point me to a good alternative filter?
Cheers all,
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