This is a Brand New Countershaft for the NV4500 Transmission it will work for either the Chevy or Dodge. The tooth Count on the shaft is 38-30-21-12 it is used with the mainshaft that has a tooth count of 39 Teeth on the Mainshaft reverse gear. This countershaft is used in transmissions made from 1990-1996. The area where the 1st gear will ride is 4.000"