Which torque wrench?
Halfords do some good quality, cheap torque drives that are accurate enough for most jobs. You will also need to buy a socket to fit each of the jobs you need one for, they are interchangeable with some socket sets but only for the larger 1/2 inch drives. They come in a variety of ranges of torque so check your Haynes manual or your owners manual to make sure the ones you need are covered by the range. I assume this is for retightening the axle nut after you have adjusted the chain, btw those guidemarks are not always the most accurate – it is worth using two parallel planks to make sure the axle is at a rightangle to the bike. EDIT: For what it is worth it is important to get the correct torque on the axle, especially since they stopped using split pins to stop the axle nut rotating, it might loosen and it is almost as bad to overtighten it and stretch the thread.
