the 310 is only really useable with a 18"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


