I was lost all day trying to find the right tools. A guy at an oreilys explained to me that now a days bikes or vehicles are either metric or standar. Standard being in fraction and metric in mm. So in the pic on the left i have a 5/15 allen hex bolt in it. It pretty good in there. I tried a T50 hex nut bolt and its snug snug in there. Like i have to apply pressure to get it in and to take it out i have to tug!. BUT the allend wrench on the right in the pic is a 3/16 and it seems to fit good