McMaster-Carr FAQ

McMaster-Carr Customers Frequently Asked Questions

Thank you for purchasing DTI SmartBolts through McMaster-Carr Supply Co.  This page provides you with additional information about DTI SmartBolts and their proper use.

This chart shows, for each McMaster part number, the Nominal Indicating Tension, the Percentage of original Gr. 8 Strength as a result of our modification, and the resulting Proof Load of the modified bolt.

GENERAL QUESTIONS

Do you make the bolts themselves?

We start with high-quality hex-head cap screws which meet SAE Grade 8 standards, then we retrofit them with our patented indicator mechanism.

What does the term Proof Load mean?

Proof Load is approximately 90% of Yield Strength.  If Proof Load is not exceeded there will be no permanent stretch of the bolt.  Correct operation of the SmartBolt indicator depends on not exceeding the Proof Load of the bolt.

What if I want a quantity discount on DTI SmartBolts?

Contact Stress Indicators, Inc. directly at sales@smartbolts.com or 240-631-7246.

What if I need metric or other sizes not offered by McMaster?

Contact Stress Indicators, Inc. directly at sales@smartbolts.com or 240-631-7246.

What if I have a question which is not answered in this FAQ?

Contact Stress Indicators, Inc. directly at customersupport@smartbolts.com or 240-631-7246.

TORQUE VS. TENSION

Do SmartBolts indicate tension or torque?

The SmartBolt indicator measures tension and allows the user to estimate the actual clamping force on the fastener at any time.

What is the difference between bolt tension and bolt torque?

Torque is the amount of force required to turn a bolt and is a rotational force commonly measured in foot-pounds or Newton-meters.  Torque measurement is affected by friction factors which may vary significantly.  Tension is the longitudinal force on the bolt and is measured in pounds-force (lbf) or kilograms-force.  Tension is the actual clamp force on the bolted joint and is not affected by friction factors.

Is knowing the tension or the torque on the bolt more important?

Tension is more important since it measures the actual clamping force on the joint, which is what holds the joint together.  Torque is an inadequate way to indirectly measure tension.

APPLICATION QUESTIONS

What is the purpose of the supplied Color Chart?

The sticker that is supplied with your SmartBolt shows the color at various levels of tension.  You can attach the sticker to a card for permanent reference.  You can access the PDF of this file here.

How should I use the Color Chart?

While in good lighting conditions, hold the chart up to the indicator.  It’s good practice to put the intersection of two colors next to the indicator.  This way you can compare the indicator color with the chart and know that it is darker or lighter than the color on the chart.  Once you reach the TIGHT color, the bolt is properly tight.

Should I use a spotlight or flashlight on the indicator to see it better?

Light directed at the indicator can make the indicator appear too red.  Better to have indirect light which illuminates the area of the head of the bolt, rather than shining it directly on the indicator.

What tension corresponds to the TIGHT color?

The indicators are designed to reach the TIGHT color at 75% of the Proof Load of the bolt.  In some cases the Proof Load is slightly reduced by our modification.  See the chart for details for each part.

What happens if I tighten the bolt beyond the TIGHT color?

If you tighten beyond the TIGHT color you may permanently stretch the bolt, and therefore the indicator will no longer operate correctly. There is approximately 25% of “head room” beyond the tight color before permanent damage occurs, but since the color change is subtle tightening beyond the TIGHT color should be avoided.

What should I check for in the bolted joint for proper use?

The bolted joint must have parallel surfaces for accurate indication.  It is preferable to use a hardened washer under the driven element (head or nut) in any case to prevent galling.

Should I use a lubricant on the threads?
It is good practice to lubricate the bolt threads and all parts that experience relative motion during tightening with a suitable grease or thread lubricant such as API 5A2, Torq/2 or Never-Seez.  This is necessary to assure reasonable accuracy when torque wrenching, and to ease tightening torques required to set the design preload by means of the DTI visual indicator, as well as to prevent galling damage to the bolt threads. 

Is it better to tighten the head or the nut?
Either may be tightened, but it is always preferable to drive the nut rather than the bolt head due to the reduced friction of the nut.

Can you use an impact tool to tighten SmartBolts?

Use of an impact tool is not recommended.  Its best to use a box wrench so you can see the indicator color as it changes.

What is the operating temperature range for SmartBolts?

Our specified temperature range is -20C to 75C (-4F to 167F).

What happens if SmartBolts get too cold?
No damage to the SmartBolt indicator will result, but it will not operate properly until operating range is reached.

What happens if SmartBolts get too hot?

Continuous operation beyond operating temperature range will degrade the indicator over time.  The loose indication will gradually begin to darken, so that it no longer gives the fully bright loose indication.  Brief spikes exceeding the temp range will not hurt the indicator, only extended exposure.  Rate of degradation depends on by how much the temperature limit is exceeded.

How do the bolts stand up to outdoor environments, rain, snow, mud, etc.?

Within the specified temperature range, your SmartBolt may be expected to perform through all normal environmental conditions.

What is the expected lifetime of SmartBolts?

SmartBolts can be expected to last for the service life of the fastener, or 20+ years.

Is there any loss of strength as a result of your modification?

This chart describes any loss of strength due to the installation of the SmartBolts indicator.

POSSIBLE APPLICATION PROBLEMS

Problem- Small red “bubble” appears in indicator after fastener has been in a tightened state for several hours or more.

Cause- Vacuum void is formed in indicator due to tightening too rapidly in the initial phase.  Most likely to occur in a fastener stored in an unstressed condition for long periods.

Solution- Loosen fastener slowly until red area just disappears or moves out of the indicator area, and then SLOWLY retighten. If left in the tightened condition, the problem will usually resolve itself and spot will spontaneously disappear.  After, at most, two or three tensionings of the bolt, the red bubble should not return.

Problem- Bolt indication no longer occurs at Design Tension.

Cause- Deformation of the indicator window ring has occurred.  Either the bolt has been dropped on its head area or the bolt has suffered a blow to the indicator ring area. 

Solution- Replace.

Problem- Indication does not return to bright red when bolt is loose.

Cause- Bolt has probably been overtightened and the tensile stress has exceeded the material yield point, or the bolt has been exposed to temperatures exceeding the limit.

Solution- Replace.