The only torque wrench I’ve seen is for tightening car wheels.
Just for general bike maintenance.

You don’t

I own a superstar components one and its fine for bike use

You dont “need” one. But this works well(2-24NM), although it’s 3/8″.

I’ve got the Sealey one above and it’s been fine.

Got a nice set of decent driver heads that I only use with it.

The Giant tool shed one has all the most common heads with it. Sixty five quid,but can be found for less.
If you have a carbon post,frame,bars or stem you ought to have one.

http://forum.slowtwitch.com/cgi-bin/gforum.cgi?do=post_view_flat;post=3345080;page=1;sb=post_latest_reply;so=ASC;mh=25