This is the hard to find firing pin FIRST model Winchester 1873 .44 and .38 caliber lever action rifle. First model 1873 rifles used a unique firing pin (1st models are generally under serial number 29,500. The way that you can tell if you have a first model bolt is If your bolt has a bushing on the face of the breech bolt projection. The 2nd and 3rd model bolts did NOT use this bushing) If you have 2nd and 3rd model you need part number 747.