How it is made. Every tray is 150 mm deep with a 3 mm floor and 2.4 mm walls, corners rounded. The side walls scoop down over the front third — a straight drop into a quarter-round, so it prints without supports. Two 5 mm pegs stand on each side wall's top edge, behind the scoop; the underside of every floor has four matching blind holes, 2 mm deep. Set one tray on another and the pegs find the holes. The top tray is 26 mm tall: a 46 mm pocket along the back for pens and two or three square pockets in front, the same holes underneath.
Sizes. Small 120 mm wide, Medium 180, Large 240. Low trays are 60 mm tall, tall ones 90. A stack of three low trays and the top stands 206 mm. One tray from $12; three from $32; three and the top from $42.