What guitar is it going on and what model of Mini do you have? If you buy a new set of Duncan Minis they have the threaded adjustment screws for mounting into pickguards.... Gibsons Minis come with the rings around them and are meant to be installed in a P90 style route and will not fit in a normally humbucker route....
If you have a Duncan set, your mini will screw into a full size humbucker ring or pickguard but have space on either side of the Pickup. I have seen guys take a piece of pickguard plastic and make their own humbucker rings that fit the screw holes of a Gibson style hubucker ring but have a smaller hole for the minis..... I'm thinking of doing this to an Epi Les Paul i own.. Cut special humbucker rings to fit Duncans Minis... That may get me closer to the sound Pete got in the 70's but on a real budget...