There was bitd a thinner Pots mod bolt. It was used on SR's and Power Stems where the top bolt dia was narrow. The pita was it was only small enough to get the inner down, so you had to chop the outter down and fit ends everywhere. A wee bit like a mountain bike cable on the rear where you only see the inner.
The way around it would be to get a hollow bolt, and open the top washer on the vectors out so it fits. I did that with a Power stem and it was ok. My sh vectors had a hollow bolt on so its a wee bit of trial and error.