Rotary cutter stumpjumper nut??

[countrybumpkin]

Need to replace the 1"-14 stump-jumper nut on my old fmc cutter, I have a new standard grade castle nut from a local hardware store but not sure if the nut should be a harden nut ? All the ones on line for rotary cutters are at least 15 dollars and black with a flange are these hardened ??

 

[Coyote machine]

For that application you could hardly go wrong using a hardened nut- BUT, I'd check with a current manufacturer and see what they use: Woods, etc.