This mini crossbow does not use any rubber bands or elastic, instead relying on storing energy in the limbs like a real crossbow. The limbs need to be printed out of PETG to allow them to flex (PLA will snap). The limbs should also be printed with 3 walls at a wall thickness of 0.4mm and at an infill of 20%-30%. The crossbow also features a 2 piece trigger mechanism which is more accurate to real crossbows. For ammunition use toothpicks cut to 50mm. Longer toothpicks do work but are less consistent. The fasteners are standard M3 screws. I use ultra flat head M3x10mm screws to make the two halves of the main body flush. The limbs are attached by M3x12mm screws and the arrow retention spring is attached by a M3x6mm screw. You can use string or any other thin rope. I used kite string because it was what I had on hand.