Every time we add stuff to the projector the cost goes up take MM1/ filter Brackets. not a real big expense but by the time you pay shipping you are looking at around 20 bucks each If you do not own a milling machine it very hard to make slots. I came up with a way of doing it for 8/32 slots not sure about 1/4 20 I have not tried this method to make that size. Ok you need aluminum angle bracket you can get that at home depot not real cheap but reasonable. you need a metal cut off saw or a miter saw (just change the wood blade out to a metal cutting blade) and a drill press.
Now measure about 1/4 inch in from the end of the stock angle bracket cut down but not all the way leave about a 1/4 inch or so at the bottom. now measure over another 1/4 inch and mark do not cut yet!!! then measure another 1/4 inch and make another slot and so on until you have made all the brackets you want. still do not cut through any of them turn it around and do the same thing to the other end of the bracket. Dont cut through any yet now take an drill bit very close to 8/32 set the angle bracket up on a drill press vice so it is vertical to the drill bit on the drill press line it up and drill it down to the end of the slot do the same thing for both sides of the angle bracket check your Allen screw to make sure it slides nice up and down. Now you are ready to cut the brackets. Oh one thing I forgot you need to take into account the width of the metal cutting blade which is just under 8/32s at least on the one I am using when you measure you need to account for that where you are going to cut the brackets so both sides of the slot come out even this is just to make them look nice and uniform I have screwed a few up, no biggie they function fine. here is a pic of the final product after some filing.