I found this thread as I was looking for info on a DIY version of this:
https://tarett.com/products/transmission-link-986-5-spd-ptlnk-01?_pos=67&_sid=bbfefe4f5&_ss=r
I'm making one for myself but using stainless for the all thread. I think it would be better to use brass but it's pricier. If you want to make your own I'm glad to share the parts I got from McMaster-Carr