This is a brass ratchet pinion for a gravity clock.  MO.45 x10.  If you look closely you will see there is a ratchet cut on one end.  Pinion diameter is 5.42mm.  Pinion length is 6.3mm and a through hole of approx 1.6mm diameter.  These pinions usually retail at £75 each.  11 pinions available.  New old stock.