Whats the part that attaches the rod of the piston to the driveshaft? ?

Sorry if its not called the driveshaft. I don't know names. But I know there's. 2 like fins that come off the rod on the piston that attach to the driveshaft(?). So my questons are 1 what are they called and 2 does they're length have an affect on transfer or power? I think I just figured that out, they'd have to be equal to the length of the cylinder right? Another question. I know transmissions do this but at higher speeds if you could shorten the length of the thing I'm asking the name off it would give it more speed then torque right? Which would be good