Blaise is probably right about the years. Since your boat is an '81 you probably need to get a serial number and call Edson. I found my Edson doc and our '79s are model number 335. The serial number is supposedly on the casting, on the top edge under the binnacle if you remove it. Not sure if you can find the page in their catalog but mine is listed "Steering Maintenance Parts List EB-204-2". It shows all the shaft, sprocket, and bearing numbers but not the chain nor the wheel. And it illustrates them for two models, the 335 and the 400.