The C90100 Pentax Extension Ring Kit is for industrial lenses. These ring/tubes shorten Minimum Object Distance of the lens. The kit includes 0.5mm, 1mm, 5mm, 10mm, 20mm and 40mm extension spacing tubes. They all have a 31mm diameter.
In the Box
Pentax C90100 Extension Ring Kit with 6 Various Size Rings, for Industrial Lenses, Shortens the Minimum Object Distance