Thanks all for replying- sorry for my delay in reply, been really swamped.
PSDX- thats actually what i ended up doing after failing to get the size from a dealer and finding out the other bolts on the rops are actually smaller. The threads in question are 5/8-18. So I bought a bolt and lockwasher and just got in from my installation.
S219- that thread is actually what put it in my mind- my forward facing lights are mounted on the inside of the bends on the upper ROPS so they are high yet protected by the rops itself. The rear light did not need to be as high so the placement is perfect. I wired them all into the circuit for the rear worklight that came on the tractor from kubota- that light mount was too low and the lens actually cracked by coming in contact with the top of my rear blade when the top cylinder was retracted fully. I used the original light mount to mount the switch- its easy to reach back and pop them on.
If anyone is looking for a good source for tractor lighting try towmart.com -i got my forward lights from them last year and the rear this year - both times they seemed to have one of the better selections and the best pricing. They were helpful when i had a question and shipped promptly.
Thanks again
Bill