Strider Harness is a common Artifact — Equipment card from Scars of Mirrodin (SOM), collector number 207. Current market price: $0.18 (foil $0.20), 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.)