Approx. 27mm overall length.

Rear thread is male 39mm so will fit (screw into) Leica screw or M39 camera.

Front is female 42mm thread so will accept M42 Pentax screw Praktica screw lens,but probably for use with VISOFLEX or bellows unit? 

USED very good quality and fully usable product. There is NO maker's name on the tube.