the 310 is only really useable with a 18" i was kiding about the 42"As for the Stihl website, it's worthless in bar selection. It's not based on power. As for the Oregon site, I'd guess it's based on bar mount pattern. They offer a 42" intended for the 066. Coincidently, it's the same mount as the 310....so technically.....it'll fit.
Jeff
stihls site says onething and the dealer says another