It kind of reminds me of part of the fuel system of an early 1900's farm tractor. In the vicinity of the float/carburetor. But honestly that's a guess from working on a 1920's John Deere in 1976.
Skamaniac's guess is similar to what I was thinking. An oiler or inline fuel filter for an early engine of some type, but that's really just a guess. If you have a few more pics that may help narrow it down.