I'm trying to reproduce an electrical toy from my youth that my dad built. It's a spinning motor and one component was an electromagnet made of a thread spool wrapped with wire and connected to a 12v lantern battery. For the life of me, I can't seem to make a magnet that's strong enough. It has to be strong enough to attract a piece of metal from an inch and a half or so away. So, was this just a spool of wire or must there have been a bolt through the middle and how can I make it strong enough? Thanks for any hints.