Patent data plates are located on the firewall of the engine compartment near the heater duct. There were two basic styles used between 1955 and 1957 models. The large data plates were used on all 1955-56 Thunderbirds and 1957 models until mid-April. The small data plate was phased in during the week of April 15 to April 19, 1957. The smaller data plates were then used on 1957 models until the end of production of the 1957 Thunderbirds Dec. 13, 1957. The small data plates starting in April 1957 did not show the destination code or scheduled Item number. On the smaller data plates the transmission type and rear axle ratio were shown following the date code.