For use with Keysight model and serial numbers: Model 66101A: 3139A-00101 and Above Model 66102A: 3139A-00101 and Above Model 66103A: 3139A-00101 and Above Model 66104A: 3207A-00101 and Above Model 66105A: 3207A-00101 and Above Model 66106A: 3207A-00101 and Above