.A screwdriver is a tool for driving screws; screwdrivers have a tip that matches into the top of a screw. Location of the fulcrum, effort and resistance in 1st, 2nd and 3rd class levers. Another type of screw known as a bolt which usually connects to a bolt. Nowadays there is a more simple solution for each industrial application like automatic screw tightening. Best chinese developer for automatic screw tightening machine already sold many machines to various production units. Contact and register your order today.