The A.P. CO mark on the porcelain insulator tube may be Anderson Porcelain Company, East Liverpool, Ohio. According to Jack Tod's "A History of the Electrical Porcelain Industry in the United States" (self-published 1977), the company started production in 1900 and was bought out in 1911 by General Porcelain Company (pgs 71-71).
Lee Bennett, RPA
Bennett Management Services, LLC
PO Box 656
Monticello, UT 84535-0656