AA12 sight mount for optics, you will need the following for this to work:
1 x AA12 Sight Mount Plate
1 x M4 Countersunk Metric Bolt (10mm long, including head)
1 x M4 Brass Insert
Please do not buy this unless you're prepared to do the work required to make this functional, this is due to Shapeway plastic not being able to take screws right away, this product link is enabled for a user who contacted me and is happy to conduct the required work themselves, you will need open up the hole yourself for the metal threaded insert in the link above.
Also please be aware that I would not recommend buying this piece in the metal versions unless you have the necessary tools to clean up the thread (an M4 tap), this is due to the detail of the thread is likely going to be lost in the casting process, it's also very expensive :(