This part is a kind of semiconductor called DB3.

Function of this product has SILICON BIDIRECTIONAL DIAC.

Manufacturers : MCC

Image and pinout :

Some of the text within the PDF file :

MCC TM Micro Commercial Components
  omponents 20736 Marilla Street Chatsworth    !"# $ %    !"# Features l The three layer, two terminal, axial lead, hermetically sealed diacs are designed specifically for triggering thyristors. • Lead Free Finish/Rohs Compliant (Note1) ("P"Suffix designates Compliant. See ordering information) • Moisture Sensitivity: Level 1 l These diacs are intended for use in thyrisitors phase control , circuits for lamp dimming, universal motor speed control ,and heat control. Type number is marked. Maximum Ratings l Operating Temperature: -40oC to +125oC l Storage Temperature: -40oC to +125oC l Thermal Resistance Junction to Lead:167oC/W l Thermal Resistance Junction to Ambient: 400oC/W Electrical Character [ ... ]

DB3 PDF Datasheet Download