Kontax are one of the better quality makes of low temperature Stirling engines.
This is a fairly conventional low temperature Stirling engine, except that it's made to a high quality standard. It's claimed to be able to run off the heat from a hand, although I've found this is only so if the air temperature is low enough. It will run on my naked thigh at room temperature! It will also run on a block of ice and, of course, a mug of tea.
It has miniature ball bearings in the crank shaft and a graphite power piston in a glass cylinder. The power cylinder is 9.5mm bore x 8mm stroke. The displacement piston is 70mm diameter x 7mm stroke.
Condition is used but almost as good as new. This example comes with the optional glass dome cover.