This is a New Old Stock Accelerator Return Spring. It still has the installation instructions furnished by FoMoCo.
We show it fits"
1965 Big Ford (Galaxie) 3x2 352 or 390
1967 Mustang 289 & 390
Some 1967 Fairlanes with V8 engine
Ref OEM # C5AZ-9737-B
Stock # P09-16420-058