Torque wrench wisdom from a 29 year retired Snap-on rep.
The digital types from Snap-on and others are the bomb, they use an electronic strain gauge, the same type of instrument used to do calibration. Nothing better for accuracy or dependability, moving parts are not an issue.
The dial indicator wrenches are extremely accurate and use a bending beam inside that is directly connected to the pointer. There is exactly one moving part, and no friction loss. They are great for extremely low torque requirements like pinion bearing resistance etc. They are a little fussy to read, and easily over torqued and damaged. Unless they are damaged they seldom need calibration.
Click type are next best, there are two styles. One has a rectangular body and a fulcrum runs along a beam to set the torque. These are generally quite reliable and are what I use. I have a 100 foot pound 3/8 drive and a 250 ft pound half inch drive.
The second style is the round body that uses a coil spring and cam internally to make the click. When you turn the handle to adjust the torque, it compresses the coil spring. Always return this type of wrench to zero when you are done using it, otherwise the spring is constantly compressed while it sits in your toolbox and it loses accuracy as a result. Accuracy is fairly good, but there are moving parts and friction involved, these will not be as accurate as the above types.
Bending beam pointer style wrenches with the indicator near the handle are very old school. They can be accurate, but fussy to read and can't really be calibrated at all. Just bend the pointer back to zero and cross your fingers.
I was constantly asked how often a torque wrench should be calibrated. The answer is how much do you use it, and how much do you trust it? Many manufacturers including Snap-on will do calibration for a reasonable fee. Snap-on's policy is that if a wrench is out of calibration and requires more than 50% of the new cost to repair it, they will not proceed and will notify you. In some cases they will even sell you a new one for half price, ask your Snap-on rep (if you are a good customer). They have some latitude, but they make money by selling tools, not so much on repairs and calibration.
There are independent calibration labs in most big cities who can calibrate and repair most major brands. Don't waste your time with Chinese junk.
A torque wrench is a precision instrument that converts friction and resistance to turning torque. The more moving parts, the less accuracy.
Never ever use a torque wrench as a breaker bar. It might be the longest thing in your toolbox, but tightening it to a load and then a fastener breaking loose and it instantly returning to zero is almost the equivalent of shoving your tranny from neutral into gear while rolling at 60 miles an hour.
Sermon over, I hope this helps.
