I'll explain the dupe to the best of my ability to those who want to know. Reminder, I am NOT a game dev, so I may be completley wrong about this. The dupe happens because whenever a saw touches a box/spring, it gives you a box/spring back and removes the placed one. But if you place a box inbetween two saws, both saws will give you the placed item. 
This is a dupe preformed correctly. Notice the box will touch both saws when dropped.
This is a dupe preformed incorrectly. Notice the box will only touch one saw when dropped, returning only one box.
Hope you found this guide helpful, Bye! :)