10fenney - I mainly use Dragon Laser fan and matrix diffraction gratings. They are 11.99 a piece, but the shipping costs are very high. But unless you want to spend serious money for gratings, they are the best value for the money. I think about a year and a half ago there was a DL diffraction gratings GB where I purchased some. But most of my DL grating I got when I ordered lasers from them so then the shipping cost were absorbed by the laser shipping cost. I also have some thin mylar ones that I mounted in old 35mm slides that I will use If you go into the LPF search engine and put in Dragon Lasers Diffraction Gratings, you will find many threads on it.