In 1895 Fred Locke sold his first order of porcelain pin type insulators for a line that ran from the Rome Powerhouse on the Yuba river to the towns of Nevada City and Grass Valle, Ca . The line operated at something like 12kV 133 cycles if I remember correctly. The original insulators were unmarked and marked Thomas made Dry process U-923c. There is some historic evidence that the Thomas made units began to fail in service soon after installation and may have been intermittently replaced with insulators of the same design made by Imperial of wet process porcelain in 1896 and 1897 . Around 1899 the whole line was re-insulated with glass CD 293 Locke insulators mounted on white glazed Victor factory made porcelain pin bases .
I personally walked parts of the line and found damaged CD 293's and a few broken bases but no cross tops . The cross tops were evidently reused locally on lower voltage distribution lines at lower voltages and occasionally turn up in antique shops in the local area as do the glass Lockes . The plant was shut down around 1912 as 133 cycle service became obsolete and converting the plant to 60 cycles was considered cost prohibitive . As far as I can determine this line is the only source of the unmarked Thomas made dry process U-923c specimens.