Chelsea platform escapement. These fit model K and 17E movements. It will not fit the ships bell or 12E movements however the balance will work in those if that’s all you need. They are used with good jewels and balance staffs. They will need to be cleaned and oiled before use. Check The Chelsea Clock Technical Manual by Andrew Demeter for more information. He is seller aka315 on eBay.
Platform measures 34.9mm x 18.6mm
Import duties are the responsibility of the buyer.