Stacking Letter Tray Corner Post
This corner post lets you build a stacking letter tray from four printed corners and plywood or hardboard offcuts 3–6 mm thick. Each corner is 36 x 36 mm with a 50 mm tier pitch. The board rests on a 4 mm pad between two 3 mm walls and is held by one M3 bolt with a captive nut. A 4 mm pin on top fits the 4.5 mm socket in the corner above, so tiers stack without glue. For each board, trim each corner at 45° with 12 mm legs and cut it 6 mm smaller than the outside size you want: 222 x 285 mm gives an outside footprint of 228 x 291 mm, which fits US Letter.
desk letter-tray paper-organizer stacking