This is a reduced power plunger spring for CZ and Canik pistols.
Very popular with Canik owners when combined with the Glock 28 Newton extra power striker spring to reduce trigger pull weight. A polish of the moving action components and replacement of the striker and plunger spring usually drops the trigger pull on a Canik down to around 3.5 pounds.
Yep, it's an expensive spring but extremely hard to find. We're still trying to source them at a better price than our first batch.