It is a digital product, what you get are STEP and DXF format files. This sliding iris diaphragm is similar to a shutter mechanism. The shape is similar to Chinese ancient copper coins-a square hole inside a circle. There are four blades.When you move the Driving Button,the blades in the center square hole open or close gradually. Most parts can be manufactured on a laser cutter. You need to prepare some metal parts,such as bolt, nut, pins,refer to the BOM in the package. The square hole is 60x60 mm, the outer diameter is 200 mm, and the mechanism's thickness is 12 mm. Part's thickness is 3 mm. STEP and DXF format files are included. Ignore the STL, OBJ and FBX format files, they are only uploaded to meet cgtrader's requirement.Free 3DPDF file are downloadable: twothreed.com.Assembly tutorials: https://www.tanerxun.com/assemble-square-hole-type-sliding-iris-diaphragm/.html