This is a motor reduction gear with 43 teeth to 26 teeth.
SPECIFICATIONS:
Diameter 43 tooth gear: 15.75 mm x 4.60 mm
Diameter 26 tooth gear: 5.90 mm x 2.98 mm
Total length: 20mm
D shaft: 2.66 mm long x 3.68 mm dia. X 2.68mm flat
Hole depth: M3x6mm threaded