David has said before that PTC frames from about 1912 to 1916 look exactly like
STC underframes built beginning in 1916, when both PTC and STC changed designs.
It's very confusing! :-)
"Why do you think the Ohio Cities Gas Co.car was built by Pennsylvania Tank Car?
Standard Car Construction Co. (STC's predecessor) started in 1915 and didn't build cars in quantity until 1916, while high-walkway cars with the stereotypical "STC" underframe appear in the ORER entries for Pennsylvania Tank Line (PTC's leasing arm) as early as 1912.