are you using spacers
That would be my guess
spacers shouldn't make any difference, the longer stud on the spacers counters the width of the spacer therefore retaining the standard nut, bolt on spacers always have a corresponding stud length again retaining the standard nut.
does that depend the the space type though
Yeah, this generally boils down to how thick the spacer is, most of the big sizes will come with the bolts needed, but as has been mentioned the bolt length will be the same as they are on the OE bits.