It’s 1/2” tubing. I don’t recall the ID, but it was smaller than what I needed to tap it. I simply drilled it to the proper size and tapped it. The heims are 3/8-24. I got left hand threads for one side so I could adjust the length with taking the bar off. It worked great compared to just having the single adjustment at the clutch fork. I sourced the tubing from an online metal supplier and bought 2’ of tubing which was plenty. The heims are Amazon specials. All in I think I was less than $25 including buying a left hand tap.
