In order to allow the baffle plate to slide back and forth, I need to slot it. However, since I'm concerned that just putting screws through the slots will create a point contact between the screw and the side of the slot and over time wear a divot in the side of the slot, I decided to make some glide washers. These will fit in slots that are just a few thousandths wider than themselves and 1/2 inch longer. The screw goes through the hole, and the glide washer has a 1/8 inch long flat area on each side. Thus, no point contact anywhere and the whole assembly should stand up to vibration for the long term. Oh, and these washers are 0.032 inch thick whereas the baffle is 0.025 thick. So when I screw through these into a backing plate, there will be a few thousandths left to allow the baffle to slide.