These are rough estimates and there are overlaps.
Silver tube, wood bottom - 1900 to 1925
Silver tube, aluminum bottoms - 1925 to 1937
Blued tube, aluminum bottoms - 1937 to 1939
Blued milled tubes, aluminum bottoms - 1939 to 1941
Blued milled tubes, plastic bottoms - 1941 to 1942
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Mike C.
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