Start eating Bike Tools Etc. - 1000's of bicycle tools and parts for the home mechanic!I could be wrong but I believe you will find that shifter housing is 4mm and brake is 5mm. Certainly that is the common arrangement. They are NOT interchangeable.
Or post a link to 5mm shifter housing and I will eat some humble pie.
Put it on eBay. Call it "vintage" or "rare". You'll have bidders falling all over themselvesThere is 5mm shift housing, no one uses it. I might see it once or twice in a thousand bikes that come into the shop. We've had a box of 5mm shift housing that some idiot ordered years ago sitting in the back cuz no one will use it. We've been using 4mm for as long as I can remember.