That's how the hood is kept on, isn't it? To remove it, turn the handle so that it's horizontal. In that position the flats on the handle-ends align with the keyways in the frame and the handle can then be eased outwards and the whole thing removed. Then the hood lifts off. When the handle is anything other than horizontal, the handle flats don't line up with the keyways so the handle stays in place and the ends hold the hood on. The entire system is simple, cheap (an important consideration for Tilley!) and foolproof - there's nothing to be adjusted or can go wrong. Machining tolerances, maybe, but I doubt it. Maybe they drifted a bit over the years so if you put a newer handle on an older lantern, or vice-versa, just possibly there might be a mismatch...
@Thomas @David Shouksmith , your description of handle horizontal and spread with your hand is exactly right for my 70's one. The '64 one needs much more persistence for some reason that I haven't figured out yet.
There is no keyways in the frame on my lamp, just clearance enough to spread the handle to remove the hood.
@Thomas I think I'm right it saying that the style of bail/handle that you have is earlier than the ones with the keyway. All my late 1950s X246s have that type of frame and bail arrangement, whereas my X246Bs have the keyway. A trip through the Reference Gallery might shed a light when the keyway was introduced. Cheers Tony
@Thomas & @David Shouksmith Mmm... Here is a 5/1966 X246B with the handle that does not separate from the cage. Cheers Tony