you are refering to screw in brake bosses, as found on suspenion forks?
these unscrew but can be really really tight.
I have used a socket screw -aka grub screw - naturally in stinaless, or a piece of rubber cut to size and pushed into the hole.
There are at least 2 different threads for the bosses so you may not find the correct socket screw - seem to recall one being some US size.
generally you need only one as you would use the other to secure your brake hose to the forks.
a socket screw yesterday.