Don’t know what car you’re driving but I think you’re just using the wrong size wrench/Allen key
My last car was a 2012 ford fiesta. The lug nuts are 19mm. The caliper bolts were 10mm and the slide bolts were 3/8.
The car before that was a 2001 cavalier. Not only did it have metric and standard bolts but the slide bolts were fuckin Allen heads.
Like literally why?
Probably because they were made by American car manufacturers and couldn’t make a logical or consistent design decision if their lives depended on it.
Like I’m not even an engineer and I’m just screaming about the dumbest decisions made by people who make more in a week than I make in a year 😭