This BETA mount was designed to modify and adapt a nFD or FDn 135mm f/3.5 lens (33mm rear element diameter) to use it with EF DSLR Cameras, along with this part:
Aperture arm for nFD 135mm f/3.5
http://shpws.me/Sawo
For more aperture arms please visit the store main page:
https://www.shapeways.com/shops/lensmounts
Follow this link to see the tutorial:
https://youtu.be/Jiv1HAlwF68