May find some df. views on that. Some say anything but stock, barrel, lock & trigger. Some say patchbox is not furniture cause it is used. Well, what on the rifle is not used. RR pipes are used, sideplate is used & serves a purpose as well as nosecap, buttplate, etc.
For me, the Furniture would be the Buttplate, Toeplate, Sideplate, Patchbox, Entry & RR pipes, Nosecap, T/Guard. Any inlay I consider a Inlay, not furniture.
Keith Lisle