The best advice is to use Loctite Threadlock fluid on the shaft threads when refitting your new props.. you wont even need locknuts if you put this stuff on. To free them up for removal, apply heat and the stuff softens and 'lets go'. It's expensive but then so are props and one bottle of the fluild will still be on your workshop shelf long after we've all gone as you only need a tiny amount. I guess you already know this but thought I would throw it in anyway, just in case.