This part is a kind of semiconductor called P6KE51A.

Function of this product has TRANSZORB TRANSIENT VOLTAGE SUPPRESSOR.

Manufacturers : General Semiconductor

Image and pinout :

Some of the text within the PDF file :

P6KE6.8 THRU P6KE440CA TRANSZORB™ TRANSIENT VOLTAGE SUPPRESSOR Breakdown Voltage - 6.8 to 440 Volts DO-204AC Peak Pulse Power- 600 Watts FEATURES 0.034 (0.86) 1.0 (25.4) MIN. 0.028 (0.71) DIA. 0.300 (7.6) 0.230 (5.8) 0.140 (3.6) 0.104 (2.6) DIA. 1.0 (25.4) MIN. ♦ Plastic package has Underwriters Laboratory Flammability Classification 94V-0 ♦ Glass passivated junction ♦ 600W peak pulse power capability with a 10/1000µs waveform, repetition rate (duty cycle): 0.01% ♦ Excellent clamping capability ♦ Low incremental surge resistance ♦ Fast response time: typically less than 1.0ps from 0 Volts to V(BR) for uni-directional and 5.0ns for bi-directional types ♦ Typical ID less than 1µA above 10V ♦ High temperature soldering guaranteed: 265°C/10 seconds, 0.375" (9.5mm) lea [ ... ]

P6KE51A PDF Datasheet Download