Size 001 = 0.5 inches (13 mm) deep by 1.5 inches (37 mm) in diameter over the coils - an original Fobco part. 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, material thickness 0.8 mm. This is a UK-made, much heavier and more powerful 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. Should you locating peg on your drill be the wrong size its usually easy enough to unscrew it and make one of the correct size.
The Size 002 spring can be ordered online here