The ML4643 from Spectrum Control is a RF PIN Diode with Forward Current 10 to 40 mA, Reverse Current 10 uA, Breakdown Voltage 300 to 350 V, Thermal Resistance 15 to 20 Degree C/W, Forward Resistance 0.5 to 0.7 Ohms. Tags: Surface Mount. More details for ML4643 can be seen below.