This part is a kind of semiconductor called 5KP18CA.

Function of this product has Transient Voltage Suppression Diodes.

Manufacturers : Littelfuse

Image and pinout :

Some of the text within the PDF file :

5KP Series Transient Voltage Suppression Diodes Axial Leaded – 5000W > 5KP series RoHS Pb e3 Uni-directional Bi-directional Agency Approvals AGENCY AGENCY FILE NUMBER E230531 Maximum Ratings and Thermal Characteristics (TA=25OC unless otherwise noted) Parameter Peak Pulse Power Dissipation by 10/1000μs Test Waveform (Fig.2) (Note 1) Steady State Power Dissipation on Infinite Heat Sink at TL=75ºC Peak Forward Surge Current, 8.3ms Single Half Sine Wave Unidirectional Only (Note 2) Maximum Instantaneous Forward Voltage at 100A for Unidirectional Only (Note 3) Operating Junction and Storage Temperature Range Typical Thermal Resistance Junction to Lead Typical Thermal Resistance Junction to Ambient Symbol PPPM PD IFSM VF TJ, TSTG RθJL RθJA Value 5000 8.0 400 3.5/5.0 -55 to 175 [ ... ]

5K3A1IB PDF Datasheet Download