m42-m42 12-17mm 17-31mm 25-55mm 35-90mm M42 to M42 Mount Focusing Helicoid Ring Adapter Macro Extension Tube for camera lens

This tube useful for lens without focusing ring. And it can be use as macro extension tube. There is no electronic element in the adapter, aperture and focusing must be manually control.
Specifications:
Front mount:  M42 screw mount female (M42 x  mm)
Rear mount: M42 screw mount male (M42 x  mm)
Length: 12mm to 17mm (5mm movement distance for focusing)
Length: 17mm to 31mm (14mm movement distance for focusing)
Length: 25mm to 55mm (30mm movement distance for focusing)
Length: 35mm to 90mm (55mm movement distance for focusing)
Focus: manually
Material:  aluminium alloy
Package included:
1 x focusing helicoid
(camera ,lens and others is not included）