Some of my bikes have nuts with "teeth" on the back of the chainrings that bite into the ring and you snug the front. Or use the correct nut tool, which I did not. It spins in the hole and a large common in the little groove wont get it started. The nut is near toast.

My other bikes have different size allens front to back so a much better system in my opine.

Any Ideas how to get that nut off, that I may replace it with a new one and perhaps get a proper tool as well?

Thanks!

Get the right tool. If you have already damaged to nut too badly perhaps a Vise-Grip type tool will help to hold the nut. I have one with long thin jaws which I use for such work. Or hacksaw/Dremel a new slot and remove it that way.

Better post a picture of both sides before you tear it up. You might need a wrench for both sides.

I got it with a pair of pliers and a quarter. But yes I will get the tool as it is only 4 bucks but the bolt sets are 20!

Hindsight.

Thanks!

I put a tiny dab of grease on the nut threads ONLY, NOT the mating faces. I feel it helps keep corrosion at bay and makes them easier to both tighten and remove.