Product review (5 stars): Three things to know about this GE washer tub nut
This is the genuine General Electric tub nut for several of their top-load washers. Three things you MUST know:

1. You need the custom wrench for it--either the cheapie linked here or the much more expensive genuine GE part--and a decent hammer to swing at it. I'd say a 3-lb. engineer's hammer, minimally.
2. If you're going to remove this nut in the course of a different repair, go ahead and purchase a replacement. Odds are good you'll tear up the original tub nut getting it off, and if it's several years old, you may even have to cold-chisel it off.
3. Tighten, tighten, tighten, TIGHTEN. Use the marks on the exposed spindle as a guide to make sure you're still tightening it. Hit it until you can't hit it even one more time. Then rest. Then come back and hit it as many times as you can stand it again. This is so important because you get a finite, and SMALL, number of times to tighten this (soft) nut before it strips and you have to replace it.