This tele converter doubles the focal length of the lens attached at the expense of two stops of light loss. The T6-2x was the earlier 2x converter, black in color, and is comprised of 6 elements in 6 groups. It is designed specifically for telephoto lenses. According to Pentax it is optimized for use at near infinity distances. It supports inner bayonet as well as outer bayonet lenses.
This is a USED Teleconverter, overall great shape, the glass is clean, there are no dents.