This is one of the diac types.
Part Number : DB3, DB4, DC34
Description : Silicon Bidirectional Diac
Package : DO-35 Type
Manufactures : Semtech Electronics
See the preview image and the PDF file for more information.
The glass passivated, three-layer, two terminal, axial lead, hermetically sealed diacs are designed pecifically for triggering thyristors. Theydemonstrate low breakover current at breakover voltage as they withstand peak pulse current. These diacs are intended for use in thyristor phase control, circuits for lamp-dimming, universal-motor speed controls, and heat controls.
The DB3 is a full-wave or bi-directional semiconductor switch that can be turned on in both forward and reverse polarities. The DIAC gains its name from the contraction of the words DIode Alternating Current. The DIAC is widely used to assist even triggering of a TRIAC when used in AC switches.
Reference Site : https://en.wikipedia.org/wiki/DIAC
Absolute Maximum Ratings (Ta= 25′ C )