Interesting stuff. We know the XN was replaced by the GF in 1940 and we also know the tank fittings changed to bolts about the same time. I don't suppose both changes were made on the same day so an intermediary is perhaps not so surprising. Unusual and very uncommon though and a very interesting lamp therefore. I have never seen a knurled NRV cap like that which makes that a real oddity and if I haven't seen one in the last 50 years then it is near unique for Tilley. Alltogether a pretty interesting and cool lamp. ::Neil::