This part is a kind of semiconductor called Q4010LT.

Function of this product has Internally Triggered Triacs (4 A to 15 A).

Manufacturers : Teccor Electronics

Image and pinout :

Some of the text within the PDF file :

U. R L. O 1639 EC #E7 Fi le I GN ZE D TO-220 Isolated MT2 MT1 T Internally Triggered Triacs (4 A to 15 A) E3 General Description Teccor’s Quadrac devices are triacs that include a diac trigger mounted inside the same package. This device, developed by Teccor, saves the user the expense and assembly time of buying a discrete diac and assembling in conjunction with a gated triac. Also, the alternistor Quadrac device (QxxxxLTH) eliminates the need for a snubber network. The Quadrac device is a bidirectional AC switch and is gate controlled for either polarity of main terminal voltage. Its primary purpose is for AC switching and phase control applications such as speed controls, temperature modulation controls, and lighting controls where noise immunity is required. Triac current [ ... ]

Q4010LT PDF Datasheet Download