Ft. lbs./(value X12 to convert to in. lbs.):

To say that a fastener is 'tight' only means that it is not loose. To say it is 'torqued' means that it is properly installed and will function as designed. Bringing a bolt to its proper torque means that the fastener has been turned past the point of drawing the components together stretching either the bolt or the material that the bolt is threaded into.

Threaded fasteners - bolts, nuts, screws, etc. - are everywhere, and all have a specific torque value that is generally based upon the diameter, material, and degree of hardness. Granted, assembling a new set of shelving has a different quality requirement than assembling a 650 HP supercharged V-twin (it better have) but, the technician always has a key part to play in the success of the job.

In fact, most of the fasteners that we work with from day-to-day are installed by 'feel'. That 'feel' is called kinesthesia. It is the body's ability to provide specific commands to the muscle groups and the monitoring of that activity with a feedback loop. This method is considered sufficient for many applications, however, any fastener critical to safety must be torqued during each assembly.

A torque wrench of some type is necessary to torque any fastener. There are several types of torque wrenches available in all sizes of square drives.

A motorcycle shop will normally have click-type wrenches of 1/4" and 3/8" square drives with ratcheting heads. Each torque wrench operates over a specific torque range. The 3/8" drive wrench in the photo has range of 5-75 ft. lbs. while the 1/4" drive has a range of 10-200 in. lbs. (.83-16.67 ft. lbs.). Together with the proper size sockets, they would cover the torque requirements of the range of fasteners found on most motorcycles.

Industries provide many exceptions to what might be considered 'common'. A propeller hub nut on a Rolls Royce Dart turbo-prop engine requires a 720 ft. lb. torque. Since the application of torque is the use of leverage and, therefore, may be proved mathematically, the shop method to torque the hub nut is to suspend a 180 lb. man from a 4' bar. Other applications require that the fastener length be measured prior to the application of torque. The fastener is considered torqued when it is stretched to a specified length.

All torque wrenches - and you are not going to like this - can and should be calibrated on a regular basis. It is best to have a testing facility accomplish the calibration once each year. An exception to this might be if the wrench has sustained a hard shock or is otherwise damaged while in use. If this happens, a calibration should be accomplish before it is used again. 

Testing facilities may be found in the telephone book of larger cities somewhere around 'Laboratories-Testing'. A torque wrench calibration will cost from $35-$50. You will receive a card showing the difference in readings between your wrench and the 'standard' held in the lab.

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Last modified: 05/26/14