Far more likely to be 12mm than 1/2". There's very little on that tractor chassis thats not metric. 1/2" may be too big for the holes in the bars.
Close enough for government work.., like I said , go to your bolts stash and find one of known size that fits. Go from there. Whatever is used should be pretty hard steel as those things can take quite a beating, esp when using heavier implements that bounce from side to side (like my 7ft Bush Hog does.)
I don't know how many times I've laid the pin on the top of the tire or somewhere on the 3 point or implement and driven away. Usually remember it and can backtrack and find it, but not always .
Same on my tractor. I was always losing the R style cotter pins though. I now just don't use cotter pins anymore. The gravity keeps the pins in place.
No nut! Just adjust the position and drop it in. One bolt is 3" and the other 2 1/2" and like I said, they stay in there where the factory pins are almost top heavy and assured to fall off without the little PIA hairpin that the heavy brush I mow will remove promptly.
