Thanks for the tips on making shell trays, Andrew (Grebneff, that is... there are getting to be a lot of Andrews on this list). I'd just like to add that the dimensions of standard chipboard trays are designed so that they fit together neatly as Golden Rectangles. Golden rectangles have the pleasing property of maintaining the same ratio of width to length, no matter how many times they are folded in half. For example, standard American stationery (8.5 x 11 inches) and most American books are in the form of a Golden Rectangle; standard European stationery ("A4 paper") and most European books are narrower and taller. I have no idea how the dimensions of A4 paper were decided upon. So, if you double the area of any tray, you get the next tray in the series, as shown here in American units. The trays should be about 5/8 inches tall. 1.5 X 2 inches 2 x 3 inches 3 x 4 inches 4 x 6 inches 6 x 8 inches The same ratios will work in any set of measurements. What are the standard sizes for metric trays? Andrew K. Rindsberg Geological Survey of Alabama