This is an Aftermarket Boss 17-7/8" Trip / Return Spring MSC07705. 

This is the longer spring that is 17-7/8". Used on the Boss Vee Plows. 

For the Shorter 15-1/2" Spring see MSC01509. 

Alternate Part Numbers: MSC07705, MSC7705, 1304716, SNP4106, 413702