40 Chain Sprocket with 12mm Bore and 9 Teeth - TRM4144_0 - Phidgets
uxcell 24 Tooth Roller Sprocket B Type, 25 Chain, Single Strand 1/4" Pitch, 19mm Bore Black Oxide C45 Carbon Steel, Keyway with Set Screws for ISO 04C: Amazon.com: Industrial & Scientific