Locate the manufacturer's marking as indicated in the below picture(s).

DANA/SPICER/EATON FRONT TANDEM

DANA/SPICER/EATON REAR TANDEM AND SINGLE

DANA/SPICER/INTERNATIONAL FRONT TANDEM

DANA/SPICER/INTERNATIONAL REAR TANDEM AND SINGLE

MERITOR FRONT TANDEM

MERITOR REAR TANDEM AND SINGLE

ROCKWELL FRONT TANDEM

ROCKWELL REAR TANDEM AND SINGLE

MACK FRONT TANDEM, REAR TANDEM, AND SINGLE