The Apollo has a threaded end cap to post the pen, the Churchill is just a press fit to post.The tubes are different sizes. The Apollo has a metal front section and a metal coupler. The end piece of the pen where you post the cap is also metal. On my demo pen, I have worn the plating off this piece.
Threads very nice like the Churchill. Not sure if threads are the same size, if not, they are real close. As like the Churchill, not a lot of material is left on the pen tube. The fountain pens writes very nice. I make both pens for my store and like both of them.