Arnold 490-850-0006 490-850-0006/bsk1 Blade Balance/Sharpener Kit. This kit extends the life of mower blades by keeping them sharp season after season. The vibration-free operation quickly sharpens blades while the static balancer easily shows if blade is balanced. Contents include one blade sharpener and one static blade balancer. This fits any 1/4 or 3/8 electric drill. Please refer to your user manual to ensure proper fit and use.