I am not sure which type, 3/8 pitch or 325 pitch. is the correct one. I have tried two types after sharpening, but both make a crooked/curved cut, which I am told means it's the wrong chain.
The pro 260 takes a 3/8 LP .050 chain. you did not say what length of bar you had. Do not try to run a 3/8 or .325 chain on this saw. The sprocket is set up for a LP chain. Other wise you are going to ruin the sprocket.