The ML4651 from Spectrum Control is a RF PIN Diode with Forward Current 10 to 40 mA, Reverse Current 10 uA, Breakdown Voltage 500 to 550 V, Thermal Resistance 10 to 15 Degree C/W, Forward Resistance 0.5 to 0.7 Ohms. Tags: Surface Mount. More details for ML4651 can be seen below.