Seth developed poles using CuNiFe (Copper/Nickel/Iron) material which was easier to machine and thread.

They also use a unique material for the poles, which was expensive at the time and is now unobtainium. They are physically bigger than standard (Gibson, also designed by Seth) humbuckers which picks up more string in the magnetic flux. The obvious difference from the outside is the size. It was designed by the great Seth Lover for Fender in the early seventies and uses several unique design qualities giving them a very hard to replicate tone using traditional materials and methods. The anatomy of the original Fender WRHB is well documented so I won't really go into it too much (I'll give you plenty of pics) here. That's another huge blog when I get time. I've done a few WRHBs before and I recently did a huge 'experiment' with lots of 'aftermarket' WRHBs including different Maxon and Fujigen made versions and some modern ones where I rewound a seventies Maxon one with several different gauges of wire to see how close I could get to an original. I'm not really into it, and I have SO little time for extra work, but if it's something cool, or for a friend I'll usually say yes. Since I got my pickup winder back up and running to make some TMI pickups I've been getting swamped with requests to repair pickups.

Coil pick up rewind machine