Snug Tight Done Right

The first step to any successful structural bolt installation is an accurate and reliable snug tight condition. Other methods and systems only suggest a vague reference for the snug tight condition with no way to quantify tension. TNA® is the only system to deliver a quantifiable snug tight condition ensuring every bolt in the connection meets a minimum requirement in the snug tight condition.

Here’s how snug works: Torque values are set in each tool model. Each tool installs a specified bolt diameter. Torque is best for snugging because it allows for steel plies to be drawn together and then to develop tension in the bolt. Pull the trigger and the tool will stop when the specified torque value is reached. Do that for each bolt in the connection. Simple, fast and reliable.

Structural bolts in any joint type (bearing, pretension, slip critical) require a first step snugging operation.  This is to ensure the plies are in firm contact with no gaps left in the connection.

Yes. Joints designed as bearing only require the bolts to be snug tight.  This is typically performed with a hand wrench or air impact tool for hex and TC bolts.  Using these methods results in joints with scattered tensions since the tensioning methods have no control over tension.  TNA® provides a consistent and accurate tension in every bolt since the process is controlled in the tool.  TNA® bolts reach a minimum tension requirement so now for even the simplest connections a known value of tension can be established.

When installation methods other than Torque + Angle are specified snugging is generally performed using a few raps of an air impact wrench or by feathering with a shear wrench.  These methods have no control over input tension so the snug condition can vary widely.  It’s not uncommon for hex bolts using turn-of-the-nut method to be installed above minimum required tension, or using DTI’s for the bumps to be crushed indicating full tension, or the tip to be removed during this operation when using twist-off type bolts.  All of these conditions can lead to false positive visual indications of tension and/or can led to bolt breaking.

TNA® bolts and the Torque + Angle Method are the best way to snug tighten structural bolts.  Here are just a few of the benefits of using the system for this condition.

  • Quantifiable -Minimum tension value when installed to the snug tight condition means every bolt will have a known snug value.
  • Accurate – Control is placed in the tool ensuring consistent and reliable snug tensions.
  • Feedback – The TAE Series tools are smart.  They provide immediate operator feedback to ensure every bolt is installed correctly.

Developing Precise Tension

Once your bolts are reliably snugged in the connection the only thing left to do is turn them to the required angle for precise final tension. Accurate angle turn is controlled by the tool, not the operator. That’s why TNA® Torque + Angle Fastening System is the best available system and method.

Here’s how angle works: After the snugging operation is completed, switch the tool to angle mode and set the dial to the required angle setting (90o/120o.) Angle is the most reliable way to produce final tension given a known and consistent snug tension value has been established. Pull the trigger and the tool will stop when the set degree of angle is reached. Do that for every bolt that requires pretension. Accurate, repeatable, and cost effective.

Yes, the TNA® Fastening System allows you to snug all the connections reliably and then only pretension those connections that require it. This will help eliminate the “bolt banging” phenomenon by not pretensioning bearing type connections. And it’s very cost effective. By snugging whenever possible and pretensioning only when necessary, you can significantly reduce your testing, installation, and inspection costs.

The fixed spline design was developed for several practical reasons. Installing from a single side with a single operator is the most efficient and cost-effective means of bolt installation. The only way to achieve that is by using a spline drive fastener. Having the fixed spline design also allows for the bolt to be installed using both modes, snug and angle. Where an operator could sever the spline of a twist-off type bolt during the snug phase, the TNA® bolt spline will not sever so there will never be an instance where tips being removed during snugging would provide a false indication of required minimum tension.

TNA® bolts are called out as ASTM F3148. This ASTM Standard is an industry approval of the fixed spline 144ksi fastener design and grade. Specify by calling out ASTM F3148 Specification. Get a copy here. Connection design can be utilized to take advantage of the increased strength over A325/F1852 and allow more flexibility and cost savings versus A490/F2280.

Bolt friction calculations should be based on F3148 minimum tension values for Fastener Tension Tb.
Note – F3148 minimum tension values are equivalent to A490/F2280. Bolt shear calculations should be based on 144ksi for Fub Ultimate Tensile Strength.

Torque + Angle Installation Method

  1. Set the tool to the Snug Mode and engage the first bolt in your connection.
  2. Pull and hold the trigger until the tool shuts off.
  3. If the cycle was completed successfully the Cycle Indicator Light will show solid green.
  4. Repeat the process for each bolt in the connection.

For larger connections, a second snug pass can be performed to ensure all plies are in firm contact and that all the bolts are snug to the same value. For connections only requiring a snug condition your work is done. For Pre-Tensioned or Slip-Critical Connections, proceed to Step 2.

After the Snug Tightening step is completed:

  1. Switch the tool to the Angle Mode
  2. Set the Angle Control Dial to the degree of rotation specified for your bolt length in ASTM F3148 (It’s 90º or 120º)
  3. Engage the first bolt in the pattern that you established during the snug mode. Pull and hold the trigger until the tool shuts off.
  4. If the cycle was completed successfully the Cycle Indicator Light will show solid green.
  5. Repeat the process for each bolt in the connection.

Your bolts are now installed to a consistently reliable tension well above the specified minimum.

Inspection after Snug Tightening

  1. Perform routine observation of the snug tightening process to verify proper techniques are followed as described in Step 1: Snug Tightening
  2. Verify that the plies in the connection are in firm contact.
  3. Verify that the proper bolt length was used. The face of the nut shall be at least flush with the first thread of the bolt and there should be no more than 3 threads stick-out beyond the face of the nut to prevent thread runout.

Inspection after Angle Tightening

  1. Perform routine observation of the final angle tightening process to verify proper techniques are followed as described in Step 2: Angle Tightening

NOTE: If routine observation is not possible, match marking for final installation may be required during the angle tightening process. This step of visual inspection should be included in the scope of work or contract documents to avoid disputes.

ASTM F3148-17a Standard Specification for High Strength Structural Bolt Assemblies, Steel and Alloy Steel, Heat Treated, 144ksi Minimum Tensile Strength, Inch Dimensions.

Within the standard you will find all of the information required to specify TNA®.  Included in the standard you will also find important additional information needed to implement the system.  In F3148 you will find Annex A1. Rotational Capacity (RC) Tests, Appendixes X1. Test and Installation Procedures for Torque-and-Angle Tensioning of Fixed Spline F3148 Assemblies, X2. Pre-Installation Verification Testing and X3. Installation Procedure.  In these Appendixes are the required Pre-Installation Verification Testing Procedure and the formal Installation Procedure.  This information is typically found in RCSC ” Specification for Structural Joints Using High-Strength Bolts”.  During the interim period prior to publication by RCSC these procedures will be referenced in this ASTM document.  When the Torque-and-Angle installation method can be included in the RCSC publication, it will be balloted for removal from the ASTM document.  This form of reference has precedence from other bolting innovations following the same acceptance path.

To obtain your own copy of F3148 you can go to www.astm.org.  For subscribers, the new standard can be downloaded as part of your subscription service.  If you’re not a subscriber, download your own copy from the ASTM site or contact LeJeune Bolt and we will provide a serialized copy free of charge.

TNA® Technology Benefits

  • A Single Bolt Grade for Every Connection Type
  • A Single Proven Coating Option for All Bolts
  • Matched Assembly Sets
  • One Tool per Diameter
  • Single Sided Installation
  • One Installation Method for All Conditions = Snug or Snug/Angle
  • Installation Control at the Tool not the Operator
  • Hands Removed From the Work Zone
  • No Pinch Point/Reaction Arm Tools
  • No Torque or Impact Transferred to the Operator
  • No Loose Splines to Cause Trip and/or Drop Hazard
  • Eliminate Over and Under Tightening
  • Eliminate Environmental Influence
  • Fixed-Spline Allows Bolts to be Removed
  • Design Using 144 ksi Criteria
  • Use Up to 20% Fewer Bolts v.s F3125/A325 and F3125/F1852
  • Save Up to 30% on Material Cost vs. F3125/A490 and F3125/F2280
  • Save Up to 50% vs. DTI Assemblies
  • Install in Quantifiable Snug Mode to Eliminate Costly Testing and Inspection Costs
  • Single-Sided, One-Man Installation to Maximize Labor Savings
  • Fewer Holes, Less Installation Time and Less Inspection
  • Less Bolting for Expedited Fabrication and Erection Schedules
  • TNA Will Contribute to Maintaining Critical Path