Reference: CMP seat back coil spring dimensions

[Grant Bowker]

As follow-up----->. The flea-market find had the end flap of the box marked:
DURO DYNE
Fire Damper Hardware
FBBKP-39
Coil Spring
Quantity 50
Duro Dyne of Canada Ltd. Montreal
The spring was wound form 0.0495 or 0.050" wire (depends on where I measured) to make a 0.50" outside diameter coil, 2-7/8" between insides of the hooks, length of the coiled portion 2-5/32"

Durodyne still exists, still has a location in Lachine (part of Montreal) http://www.durodyne.com/ A quick check didn't find the springs on their website but I'd be happy to be shown the link.