Really a torque wrench might sound like something pretty simple, and for the most part it is. However a torque wrench can be absolutely critical if you are ever going to consider building an engine or doing any kind of differential work. A torque wrenches accuracy may vary with age or abuse, so be sure not to buy a used one unless it has been recently calibrated, or you know where to get one calibrated.
What a torque wrench does is actually very simple. It operates much like a regular ratchet in many cases, but as the bolt get tighter the torque wrench will measure the amount of torque that you are applying to the fastener. This is critical for fasteners that are securing bearing surfaces, as the tighter the fastener is the smaller the bearing clearances may be. Some torque wrenches simply make an audible noise when at the set torque limit, while others use a needle and pointer gauge to determine the amount of torque being applied.
When shopping for a torque wrench, please follow my general guidelines for all plated tools. Make sure that the chrome of nickel plating is uniform and even in its thickness and appearance. Be sure that there are no sharp edges on the surface as these may indicate flaws in the plating or machining process, or worse yet, that the tool was made out of inferior materials. I typically prefer a slim design, audible style wrench. There is no reason to buy a wrench with a digital readout unless you get really deeply involved with car work, but that’s for another article all together.