These tubes consist of  front and rear bayonet components which screw directly together, plus 3 threaded insert tubes of different lengths. The different tubes do not bayonet together as with auto extension tube sets. As there is no data transfer between front and rear bayonet, the set only allows manual use.
NOTE: 
EOS tubes will have to be used with the lens at full aperture. Aperture priority can be used.
NIKON tubes will not allow ANY metering with certain bodies. Also, lenses without aperture rings will set to minimum aperture.

These tubes do provide an inexpensive introduction to macro.