I have a cheap Strat, and I was just wondering to upgrade the bridge single coil to a bridge humbucker. Unfortunately, I bought a Tenayo Hot Rail Humbucker in Single Coil Form, which is - as it states - a "middle position" humbucker. Now, should I install it on the bridge position although it is a middle pickup, or not? What is the difference between bridge and middle pickups?
You'll probably want one made for the bridge in the bridge. Near the bridge the strings don't vibrate as widely so won't induce as much signal. To compensate bridge pickups are generally "hotter" than neck/middle pickups.
That means the bridge pickups generally have more windings around the magnets which means more current induced in the wire, which would also be the case with a larger magnet, but if the magnet is too big it affects the vibration of the string too much... lots of possibilities between magnet size, type of magnet, number of windings, and even the type of wire being wound (though I think it's almost always copper)... anyway, thus the enormous selection available of different pickup brands and models. (Thanks Wheat Williams for suggesting additional discussion).