aluminum alloy, which does not damage the telescopes thread, and the 2-layer thickened aluminum alloy is very firm The M42x0.75 thread is divided into inner and outer with a double-layer structure. The relative positions of the inner and outer rings are fixed with 3 screws, which can easily adjust the camera Full manual manual for focus, manual exposure, priority exposure The adapters are made to insure the This adapter gives you the ability to use your irreplaceable lens and saves you the cost of purchasing new lenses