Graflex Raised section in tube????? Noob builder.

Hello all, I am new to this forum but I am looking to make a graflex saber replica and have a question. I have a small machine shop were I can do some work and also have access to a few CNC machines. I was looking over the original graflex flash tubes and notice that around the button and eye on the top of the flash tube there is a raised circle in the tube. My question is how was this originally done? It this somehow stamped into the tubing? If so what is the process for that? Or was it machined that way from a thicker piece of stock? Any help is greatly appreciated!

stamped/pressed

Thanks to James Kenobi 1138 for sending me this info it's called a shoulder puller: http://www.therpf.com/showthread.php?t=238694

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grenater thats exactly what I was looking for! Thank you so much for the help!