Hi Mike. I didn't post any because it varies with frame end bar thickness. The best advice is to measure several completed frames to get the width. You want a good, but not too tight fit. Glue will build up on it, so you need about a sheet of paper thickness to spare. The other dimension is whatever it takes for 10 bars to stand side by side, or make it bigger if you want, but I find 10 is a nice size to handle. As for depth, about 4 inches works well for mediums and should still work for deeps. I got lucky on mine and it works out perfectly to allow the brad nailer room for that nail under the top bar. Be sure and wax it well so glue doesn't stick permanently.
Another trick, you can use a 1" or so dowel instead of the flat bars to hold the end bars. It's easier to drill a 1" or so hole for many people than to cut slots.