How do i insert a part then place it 'x' away from a face while running parallel to another?

Hi all,

For example, if i had a bolt, how do i add a nut onto the the bolt 10mm away from the end of the bolt while keeping it inline with the bolt?

i am trying to put 4 brackets on a flail mower, and position them at certain distances apart. i can get them fitted to the outside of the mower but cant move them into place without them rotating and i'm unsure how to move them at certian distances.

Cheers