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 an inner and an 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 angle Full manual manual for focus, manual exposure, priority exposure This adapter gives you the ability to use your irreplaceable lens and saves you the cost of purchasing new lenses The adapters are made to insure the