This part is a kind of semiconductor called 1N4748A.

Function of this product has Zener Diodes.

Manufacturers : Fairchild Semiconductor

Image and pinout :

Some of the text within the PDF file :

1N4728A - 1N4758A Zener Diodes 1N4728A - 1N4758A Zener Diodes Tolerance = 5% April 2009 DO-41 Glass case COLOR BAND DENOTES CATHODE Absolute Maximum Ratings * Ta = 25°C unless otherwise noted Symbol Parameter PD Power Dissipation @ TL  50C, Lead Length = 3/8” Derate above 50C TJ, TSTG Operating and Storage Temperature Range * These ratings are limiting values above which the serviceability of the diode may be impaired. Value 1.0 6.67 -65 to +200 Units W mW/C C Electrical Characteristics Ta = 25°C unless otherwise noted Device 1N4728A 1N4729A 1N4730A 1N4731A 1N4732A 1N4733A 1N4734A 1N4735A 1N4736A 1N4737A 1N4738A 1N4739A 1N4740A 1N4741A 1N4742A VZ (V) @ IZ (Note 1) Min. Typ. Max. 3.135 3.3 3.465 3.42 3.6 3.78 3.705 3.9 4.095 4.085 4.3 4.515 4.465 4.7 4. [ ... ]

1N4748A PDF Datasheet Download