Strider Harness is a uncommon Artifact — Equipment card from Oath of the Gatewatch (OGW), collector number 167. Current market price: $0.07 (foil $0.10), TCGplayer market prices via Scryfall.
Equipped creature gets +1/+1 and has haste. Equip {1} ({1}: Attach to target creature you control. Equip only as a sorcery.)