The 21452 is a Genuine OEM Removable Trip Edge Spring Assembly Western Fisher SnowEx. 

Note: There is more than one version of this spring so make sure it is the one you need before ordering. The plows listed below may use this on some years but not on others. 

Fisher: Both Straight and V Plows, MC, LD, XBlades, Xtreme V, XV2, Trailbalzer UTV, HT, HD, EZV

SnowEx: V Plows, UTV V, HDV

Western: V Plows, Impact UTV V Plows, MVP, MVP Plus, MVP3

This DOES NOT include the shoulder bolt for the bottom.