#1 1930s, the very best, machined the backs, production ended in 11959
#2 and #3, not lathed for calibration
#4 set 1.5" bore, among the rarest
#5 started production in 1959, plates had a bore of 1-21/64" to fit the 1-5/16" sleeve perfectly, highest production numbers.
#6 same as #5, but with shorter bar

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