Here are the measurements of the spring on my C8 1940 front seats.
Rings (9 per seat)
Wire thickness 3mm
Overall diameter 25mm
Centre springs (18 per seat)
wire thickness 1,5mm
40 coils
Outside diameter 9,5mm
about 85mm overall length including the hooks
top and lower springs (6 per seat)
wire thickness 1,5mm
48 coils
Outside diameter 9,5mm
about 94mm overall length including the hooks
The top 3 springs and lower 3 springs are longer than the ones in the centre.
Rings seem to be welded at the end....it's not solder as I heated one and nothing melted....except the skin of my finger
My seats don't have the springs as shown in Peter's picture (with one long hook)....maybe a difference in supplier at the time?? or Ford vs Chev? early vs late?
Alex