This BETA product was designed to modify and adapt a FD 50mm f/1.4 S.S.C. to use it with EF DSLR Cameras, along with Aperture arm
https://shpws.me/SmN4
The mount has a gap because Shapeways 3d printing limitations.
This product needs to be separated with a hobby knife.
For more aperture arms please visit the store main page:
https://www.shapeways.com/shops/lensmounts