This is a optical post / base compatible with M6 threaded optomechanics.
There are 3 height variants available: 16.5mm (small), 41.5mm (medium), 66.5mm (large)
The height can be increased by adding further elements or mounting the post in a variable 3D printed base. These mechanics can be also used with DIY-Optics.com optics holders.
It comes with one M6x8 set screw to mount it to other standard optomechanics.