The Common Flangetail (Ictinogomphus decoratus) is one of the biggest dragonflies (about 12 cm long) that I have seen in Thailand.
The male is black with strong yellow markings along the thorax and abdomen.
The markings of the female are only slightly different to that of the male.
The face is yellow and the eyes are blue/green.
The end segments are "club" like.
This is the subspecies Ictinogomphus decoratus meleanops.

A male. Koh Lanta, Thailand, 29 January 2013