My best information is between 3.325 and 3.330. I just went into the shop and measured one at 3.312. It has probably been milled. I measured another that was on an engine, and it was a bit more difficult to measure, but I gotabout 3.3??. That's the best I can do for you right now. I hope it helps.
Motorbill
From Lola to Land Rover, If it's British and has wheels, it's likely I've bloodied me knuckles thereupon