I have one of these: Wheeler Firearms Torque Wrench. It works OK but setting a value is imprecise. Accurate torque wrenches tend to be expensive but, if you're testing and torquing, the end result will tell you what's the best and whatever wrench you're using, note the reading. Torque wrenches, if used a lot, require recalibration. Here's a bunch at Amazon and the Harbor Freight one that stangfish linked to would probably be as good as any inexpensive torquer.