Hi Brian,
To answer your question, both vulcanite and amber stems were commonly threaded, using a threaded bone tenon, during the 19th and early 20th centuries. By 1917, the practice would have been dying out, though I've seen pipes with hallmarks as late as the early 1920's that still used a bone screw-in tenon. By 1917, Barling was using friction tenons, so this is not a Barling. As early as 1912, and more likely earlier, Barling was using a combination of a vulcanite friction tenon attached to their amber stems for mounting, so the thread would not be an indicator of a Barling origin in any way.