Plumbing vent stacks in old houses are commonly made of cast iron. Today they use ABS plastic pipes. Common sizes are from as small as 1.25″ to about a 3 or 4″ maximum pipe diameter. When they did the cast iron in the old days the pipe lengths joined at “knuckles”. This knuckle is where the cast iron flared out to accommodate the insertion of the adjoining pipe. These joints were usually unnoticeable in the walls or certainly below roof level so it never effected us roofers. Once in while we run across a knuckle junction above roof deck level which means we need to do some custom lead work with our plumbing vent stacks. This particular one, on a Heritage home in Vancouver, required a custom made 6″ lead, to clear the knuckle, tapered down to a 4″ pipe. Lead is malleable and we take full advantage of that physical property. The finished product looks and works great.