I used 1/2 bore, 5/8NF heim joints. The 1 1/4" aluminium round stock is ready made to tap 5/8. I used nuts drilled to 1/2" for spacers. Of course the 12mm bosses are all drilled to 13mm or 1/2". This set up has been on the car for about 3 months now w/o problems. I immediately noticed the increased flexibility and stiffened shifts since the OEM arms are rubber mounted