Bone Sabres is a rare Artifact — Equipment card from Warhammer 40,000 Commander (40K), collector number 88. Current market price: $4.79, TCGplayer market prices via Scryfall.
Whenever equipped creature attacks, put four +1/+1 counters on it. Equip {3} ({3}: Attach to target creature you control. Equip only as a sorcery.)