I have used a spanner it looks like this..
or you can use a socket which looks like this..
along with the handle...
and hold the nut from behind and tighten the allen bolt with this..
It is a very simple task..If have trouble doing it come down to FBD I will show you how it is done.
I agree that self tapping screw are a good but till the place holding them is good. As when tighten in a wood I dont see them hold for long. As I tighten the subs self tighting screw quite often which get loose due to normal usage.