Beattie Intenscreen Bright Focusing Screen for Mamiya C220 TLR Camera (grid)
This is an aftermarket focusing screen for the C220. It is substantially brighter than the stock screen. Dim focusing screens are a problem for a lot of people with vintage TLRs and if you are having trouble focusing then this is what you need. It will likely fit other Mamiya TLR models, though I am not sure which. I do not think that it fits the C330.