A 2x Teleconverter for Pentax K and KA mount bodies and lenses. Attaches between body and lens for 2x lens focal length conversion.
This particular item is in great condition mainly, probably, because it spent its life in a Gloucestershire university campus lab attached to a microscope and a Ricoh KR-10 Super and used by the professor there.
No fungus or hazing. The rear cap is present but not the front cap, which would be identical to any PK body cap.