METAL OUTER BOWL
About the same time as Dr Kirsten , George Ash in Washington DC was working on a metal shanked pipe. In 1938 the Ashcraft Lifetime Pipe was launched. Like all the aluminium pipes, the War stopped production for the home market and in 1946 it restarted.
This time there were four models, one with a briar bowl with metal insert, which can be discarded and the pipe smoked as a briar bowl. Another was an all metal double shell bowl, the model shown here. The inner shell is removable for cleaning. The two shells do not contact each other, a wooden ring separates them. The bit is of vulcanised rubber, the bowl has 7 holes in the bottom.
An Oom Paul version produced Nov 1946 “Chin Rest” added an extension to bowl of Duoplex, and use curved bit.
More details and images under Ashcraft Screw thro bowl as that is my actual example, the plain briar bowl
Check out US Patent D144,346, April 9 , 1946 and also D144,345 April 9,1946