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Measures tension not torque,

Patented whole echo method,

Graphs tension changes in real-time,

Instrument is built into the PC,

  13.3" Color TOUCHSCREEN
ToughBook Open & Closed

Friction varies too much, bolt to bolt,

Not fooled by friction variations,

Using lubrication still leaves large friction variations,

Avoid flange leaks,


Prove to safety you took a reliable tension reading,

Far greater reliability,

All other bolt gages are one-point bolt gages,

No more zero-crossing peak jumping,

ALL other bolt gages have problems with peak jumping,

Dramatic improvement due to a new patented DSP technique,

Proven by NASA,

Can record over a million bolt tensions with their waveforms,

Playback built in,

Excel compatible data files,

Flange bolts easily grouped together,

Critical bolts,

Verify your design,


Tension verification,


Much easier to use,

Graphical help,

On-line help,

Dynamic help,

13" Color Screen instead of 5" black & white screen,

Full keyboard instead of a few cryptic keys,

Record field notes with your tension data,

You can use long file names,

Large on-screen buttons,

Familiar WinXP/2000 operating system,

Full featured laptop - Panasonic Toughbook Model 72 computer,

1 year limited warrantee,

No need to transfer data to another machine,

No hidden information,

To sum it up, vastly easier and more reliable.

Press here for a detailed point by point comparison to all other bolt gages.

 Friction and Its Challenges Confirmed By Others


By Spiralock and Lake Erie Screw Corporation

(Again we quote from other websites with excellent technical information regarding bolted joints, and recommend that the reader visit and study these sites.)

"Torque and How to Use it Correctly

The most common term used when installing fasteners is "torque". Under normal circumstances, a person tightens bolts by using a suitable wrench and if a tightness specification is given in ft-lbs., a torque wrench is used to indicate that the specified torque is reached. In reality, all that a pointer on a torque wrench dial indicates is the resistance to turning when mating two threaded surfaces. Approximately 50% of the applied torque is wasted in overcoming the mating friction under the head, 40% is friction resistance in the threads, and only 10% of the total ft-lbs. exerted produces the tension in the bolt. As tightening proceeds, a maximum torque value will be attained, followed by a sharp decrease in torque as additional turning is attempted. The decrease in the torque is an indication of loss in tightness; the bolt was overloaded and the maximum bolt strength exceeded.

So far, it has been explained that steel acts elastically within a wide range of applied loads. The elasticity property which allows a screw to return to its initial length upon unloading, ceases at the yield point.

As the bolt is being tightened above the yield point, a permanent elongation starts to set in prior to reaching the maximum strength which the screw can sustain. As the result of such behavior the clamping force which is produced from the tension as a torque is applied increases proportionally faster in the elastic range. Above the yield point, the rate of increase of the clamping force diminishes with increased loading, since the tightening energy is wasted in the permanent stretching of a screw. It is recommended that a screw be tightened, either to a load just below a yield point, or slightly above, but not to limits too close to the maximum strength of a screw since a tightness might easily be lost due to the rapid stress affects on the internal microscopic structure of the steel. The load levels at which yield occurs is different for each grade of bolt. As the strength of steel increases, the yield point increases correspondingly, meaning that the bolt's ability to carry higher loads is enhanced. Therefore, Grade 5 steel capscrews have a higher yield point than Grade 2 capscrews, and can be tightened to carry greater service loads. The same applies to Grade 8, where much higher loads can be applied than to Grade 5.

The next thing to be concerned with is the assembly load which is to be sustained by the mating members. The fastening members must be tightened to loads which exceed the carrying load of the assembly, otherwise the fastening parts may either fail during the installation or subsequently during the performance in service. Usually, a load is either static (not moving) or dynamic (joint is moving in service) where the joint load is acting either in shear or in tension.

Whatever the case may be, a designing engineer expresses a joint load either in lbs. or psi (pounds per square inch). When a bolt is tightened, the resulting load exerted by the bolt should exceed the expected assembly load and have the bolting members acting on the expected assembly load and have the bolting members acting on the joint assembly rather than the joint assembly acting on the fastening components. This is a basic concept similar to a person attempting to lift or carry a load. Unless an individual is strong enough to overcome  the weight of an object, he will either drop it or not be able to lift it up at all. The same principle applies to an assembly joint which is to be tightened. A failure to properly secure the components will occur and the purpose of fastening will not be achieved if the bolts are not capable of tightening to loads higher than demanded by the assembly joint. This is where the accurate stress state analysis of the assembly members and the selection of the proper grade of bolts becomes critically important.

The real problem in tightening arises when suggested torque values are indiscriminately applied without due consideration of the elements discussed above. Reaching such a torque on a dial gauge means absolutely nothing unless the corresponding tension is measured with respect to the requirements of the assembly joint. It has been established above that a bolt during continuous tightening experiences a maximum torque and then decreases rapidly in value until a failure occurs.

Torque measures resistance only. As one continues to turn a nut, resistance increases indicating rising torque values on a dial gauge. The resistance comes about by the tension forces which are created as a bolt stretches under an applied load. The magnitude of the resistance forces which produce the clamping force are equal and opposite in direction to the stretching force (tensile load). Therefore, we are interested in the resulting clamping load which is produced as we begin to tighten at various torque values.

To summarize, once a bolt is snugged, every turn of a nut produces an increase in torque resulting in a longitudinal stretch of a bolt which creates the pulling back effect (similar to a stretched rubber band), and clamps on the component members of an assembly. One should not exceed tightening beyond the allowable limits because the pulling back effect is lost and the clamping load on the assembled joint is deteriorated.

The surface finish of a bolt plays a determinant role on the clamping load. For purposes of fully appreciating the correlation between a torque and a clamping force (tension), keep in mind that torque measures resistance to turning. If the resistance is expressed as friction, then all one needs to do is lubricate the surface and the friction-resistance is decreased. But, this is of no help unless the installing mechanic can make an association between the torque applied and the clamping force produced so that the fastening components are put within the allowable tension ranges for the optimum performance in service. Therefore, one must by pre-testing determine for each existing surface condition, the torque range which will produce the appropriate clamping force - tension. There are available instruments on the market which will correctly correlate the TORQUE-TENSION relationship and prevent costly repairs and unnecessary downtime.

Let us take a bolt of an arbitrary size and decide to make one to nearly perfect dimensional tolerances and smooth thread surfaces; one with poor dimensional tolerances and irregularly rough threads; and one with a plating (for example cadmium) applied subsequent to manufacturing.

If we apply 40 ft.-lbs. of torque to each sample, the resulting clamping loads will be in the following order: Rough Sample: Low Smooth Sample: Higher than rough Plated Sample: Relatively the highest

The above results illustrate how premature failures come about if one strictly relies on a torque reading as the final measure of tightness. To get equivalent clamping force - tension on the above samples, one must determine the torque values for each condition, so that the clamping forces are uniform in each case.

Torque to be applied can be calculated by using the empirical equation:   KDW  Where: T=12   

T=Torque  K=Friction Factor  K=0.20 for Non-Lubricated surfaces

K=0.15 for Lubricated Surfaces

Note: Other values for K are possible where different surface conditions or additional lubricants are used.

D= Nominal bolt diameter (in.) W= Bolt Tension (lbs.) (Clampload or Preload) where W= 70% of the proof load (lbs.) (Proof load value listed in SAE J429)

When calculating for a plated condition, substitute 0.15 for K and T becomes 263 ft -lbs. It is, therefore, shown empirically that lubricated fasteners (plated or otherwise) are to be torqued at a lower value, otherwise excessive clamploads and failure during the installation will result.

The empirical equation can be put to practical use only where K conditions are properly determined by the user, and the assembly conditions evaluated.


Spiralock Reprinted with permission of Lake Erie Screw Corporation"


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