The 1157 bulb is the dominant turn signal specification across the Chevrolet C70, appearing in both front and rear positions for the majority of listed model years, including 1960-1961 and 1979-1983 (front), as well as 1985-1988 for both positions.
The 1157 is a dual-filament bulb rated at 12V with a 21W high-filament and 5W low-filament output, mounted on a BAY15d bayonet base, and standardized under ANSI specifications for the US and Canadian markets.
The 2057 bulb shares the same BAY15d bayonet base as the 1157 but operates at higher wattage, rated at 26.9W on the high filament and 8W on the low filament, making it the brighter of the two ANSI-standard types listed in these specifications.
The Chevrolet C70 (1984) is specified with the 2057 bulb in both the front and rear turn signal positions, distinguishing that year from the surrounding model years in the dataset.
The 1983 rear turn signal position is specified with the 2057 bulb, while the 1983 front turn signal position uses the 1157, indicating that front and rear fitments were not always identical within the same model year.
Although the 1157 and 2057 share the BAY15d bayonet base, the wattage difference between the two types is a relevant fitment consideration, as the 2057 draws more current on both filaments than the 1157.