If you ordered a 606607 piston from Tulsa then you will be getting a 2 ring piston. I just ordered 3 from there and recieved them yesterday. A good looking piston to I might add, I just hope that it will last like the original OMC pistons. The ring gap checked good (.015-.025). What Brad said is exactly right, the 3 ring piston and 2 ring piston are not interchangeable. If you want to convert from the 3 ring to the 2 ring piston, or vice versa, then the connecting rod would also have to be changed, the wristpin on the 2 ring setup is slightly bigger than the 3 ring setup. Not sure why anyone would want to convert from a 2 ring to the 3 ring though, since the 3 ring does not have the needle bearings in the small end of the connecting rod. Most folks convert from the 3 ring to the 2 ring because of the wristpin needle bearings, and it enables the motor to be run at 32-1, instead of the 16-1 that was recommended with the 2 ring piston. From my experience with these old 16-1 machines is that with the plain bearing wristpin, it causes the hole where the wristpin goes through the piston to become elongated, whereas with the 2 ring piston the wristpin doesn't really rotate against the soft aluminum piston boss, so the small end of the connecting rod will last much longer with the needle bearings installed.