This is a used mower deck tension arm spring from a Honda HT-R3811 and HR-R3009 with 38" and 30" decks.  Fits other models as well, use the part number as your guide. Light grime and surface rust but still works as intended. Slight bend on the one attachment point but does not effect use. New these are over $28, get this one for less!

SPRING, TENSIONER ARM
76122-751-000