What's the IMPACT C3 Delrin Spec?

Specs are somewhere around 7mm o.d. by 3mm i.d. hole and 1.5mm thick. The i.d. is what locates it centered on the rod, and is the most important measurement. If you can only find something that is 8mm it will work but you will have to trim it downloaded. The thickness isn't really an issue either, as long as it is not too thin. I made one out of a credit card that was .75mm but the plastic didn't hold up. I also tried a 4mm thick washer for an experiment, and nothing changed as far as FPS goes. You will have to change the hammer spring tension screw on the power wheel adjustment to compensate for the thicker or thinner delrin washer.

Where can they be purchased. I find good availability of delrin washers but not the correct size. 

@Fallguyz I made mine out of the edge of a 1" nylon washer 1.5mm thick from the hardware store. I used a leather punch die in a drill to cut the outside diameter, and a 3mm bit for the center hole. Any drill bit that is close to 3mm+ will work. It can fit a little snug on the valve stem shaft, but shouldn't be sloppy loose. If you don't think you have a way to cut the outside diameter, a set of big nail clippers will clip down the outside diameter fairly round with a little bit of work, as this isn't the critical diameter.

Don't go much past 7 mm outside diameter....if you do,it will be too big and hang up.