I'm not sure I understand your situation. The speedo cable in my 38 is similar to all I've seen in that it's square and about 1/8" across. I don't understand the 3/8" thing. Are you talking about the metal housing the cable runs in?

Save a life, adopt a senior shelter pet.
The three main causes of blindness: Cataracts, Politics, Religion.
Name your dog Naked so you can walk Naked in the park.