I designed these boxes to hold 100 rounds of 9mm bullets each. 10 8mmX2mm magnets are optional for the lid and box. Also included is a simple base to hold them upright. These ammo boxes should also hold 50R generic plastic trays from most manufacturers but I designed a 50R tray that you can duplicate. My Gold Dot trays fit perfectly. I printed mine in PLA+ (pictured). The box and lid are keyed so I recommend using supports for the box.