Size 001 = 0.5 inches (13 mm) deep by 1.5 inches (37 mm) in diameter over the coils. For lighter-duty machines with up to 0.5 inch drilling capacity and as originally as fitted to the Fobco "Star" Drills
If the spring would fit into the housing on your drill but is not wide enough, consider using two set side-by-side. If too wide the spring can be reduced in width (with care taken not to over-heat it) by using a horizontal band sander.
The size 001 spring can be ordered online here

Size 002 = 0.75 inches deep (19 mm) by 2.45 inches (62 mm) in diameter over the coils A much heavier spring for drills and millers with a 1-inch drilling capacity and originally intended for use on the Fobco 7/8 and 10/8 drills. If the spring is too deep for your housing it can be reduced in depth (with care taken not to over-heat it) by the use of a band sander.
The Size 001 spring can be ordered online here

The size 002 spring can be ordered online here