Not knowing anyone in the know, I took my Renthals to an engineering shop to be tapped to take the stock barend weights. He said it needed to be pre- drilled before being tapped, resulting in half an hour workshop time, which wasn't cheap. My pal who doesn't live locally to me, took his to a mate who had the correct tap, and he proceeded to just offer up the tap without pre-drilling. Job done and only cost a few pints. Result!!.