(F-Crown) PATENT/DEC.19.1871 (F-Skirt) A.U. (R-Crown) 1 SB
This early piece was manufactured by Hemingray for A.U. (American Union). It bears the December 19, 1871 patent date, and also has a "1" embossed on the rear crown. The only other insulator to bear a "1" is CD 131.4.