The ML4644 from Spectrum Control is a RF PIN Diode with Forward Current 10 to 40 mA, Reverse Current 10 uA, Breakdown Voltage 400 to 450 V, Thermal Resistance 20 to 25 Degree C/W, Forward Resistance 1 to 1.3 Ohms. Tags: Surface Mount. More details for ML4644 can be seen below.