windshield wipers

I'm trying to install the new windshield wiper arm I bought for the right side of the gasser but the special nut that holds it in place on the shaft does't seem to be starting easy---like wrong thread.Did these HAVE different thread(dif.models/years etc.)??This nut came with the new wiper arm/wiper. The original(s) that came on the truck took up residence in the the ditch along the highway recently.The left side doesn't have a nut holding the arm on--looks like same set up as on like a 85 Chevy Pick -up.

Well, I guess thats a sign of getting old---the under side of the shaft(I was looking down from above,standing up in the open cab)had some buggered threads that my old rusty eyeballs didn't detect before.Opps my bad--chased the damaged threads and we fixed.We are wipered now--and if I can get heatered too,I may be able to extend my Deuce Driving Season.

Maybe a tap is in order.

Yep-- we got'er done--Ran a thread cleaner-upper over the end and got the nut on it-- now that wiper motor has decided to simply go to one end of it's travel and stay there--no back and forth action at all.May take it off and clean/take apart and check. Got the good wiper on the Drivers side so at least I can see to get it moved around the place.