2.5mm nuts are a pain to screw onto bolts.  Especially nylon standoffs, which can put up some resistance.

This tool allows you to slot in a 2.5mm nut, place it over the bolt, and twiddle away until it's in place.  The shaft of the bolt can also extend into the twiddler, in the event that you have more things to mount atop the nut.

I'll probably add a 2mm and 3mm at some point, so shout if you need one :).

Now, get twiddling your nuts!