• Z-156-0006
  • Usually ships in 1-2 weeks



  • Range: 1/2in up to 50ft (15.24m)
  • Resolution: ±0.00001 inch (0.0001 mm)
  • Auto calibration for system zero
  • Built in load calibration toolkit
  • Large 110 dB gain range
  • 4GB internal SD memory
  • Display options: A-scan, large digits, alarm limits bar
  • Hi/Lo alarm limit used for for tolerances

What's in the Box

  • Couplant
  • 10ft Lemo to Microdot cable
  • AA batteries
  • USB Cable
  • Manual
  • Carrying case


The Dakota Ultrasonics Mini-Max bolt tension monitor can ultrasonically measure the actual elongation produced by tightening a threaded fastener. This bolt tension monitor allows you to effectively monitor your bolts during periodic shutdowns over the service life of the fastener and visually compare the unloaded and loaded waveforms. The Mini-Max can measure bolts 1/2″ up to 50 ft (15.24m). The square wave pulser is selectable in 100, 150 and 200 volts. It features a large 110 dB gain range and a resolution of ±0.00001 inch (0.0001 mm).


This product can be used in the following applications:

Here's how some of our customers use this product...

Extreme Precision Bolt Lengthening

The Background: Our customer is an aerospace company that needs to monitor the elongation of a new type of bolt under stress as part of their testing protocol.

The Problem: The bolt is a proprietary alloy designed for optimal strength to weight ratio. The engineers need to test bolt elongation down to less than one thousandth of an inch (~0.00099-inches).

The Solution: The Dakota Mini-Max Bolt Tension Monitor will meet this resolution requirement. Given the length of this bolt, about 5 inches, this will require the customer to eliminate all possible error effects due to transducer placement and installation. For these extreme applications, Dakota has developed glue-on transducers that remain firm once the glue sets. This removes the human element of holding the transducer still and with constant pressure. The glue can easily be softened with a solvent so the transducer and, more importantly, the bolt can be put back into service.

Monitoring Bolt Elongation in Critical Assets

The Background: Our customer is a power plant that needs to monitor the large bolts that hold together the steam turbines for signs of stress

The Problem: The steam turbines, perhaps the most critical part of a power plant, utilize a number 2-inch bolts that hold the turbine together. As the turbine spins and generates electricity, these bolts are subject to a huge amount of force. Failure of a bolt would be catastrophic so our customer wants absolute certainty that the bolts are structurally sound.

The Solution: This is a typical application for the Dakota Ultrasonics Mini-Max Bolt Tension Monitor. The MiniMax measures the actual elongation produced by tightening a threaded fastener and includes temperature compensation probe which creates a constant temperature reference point for all measurements. With all variables removed, the change in bolt length can be accurately interpreted by the customer.

The MiniMax is available with both magnetic and non-magnetic style probes to help reduce human error where possible. The magnetic probes hold steady in place while the measurement is made, further reducing error on ferromagnetic based bolts.

A complete kit would typically consist of a combination of magnetic and non-magnetic probes, temperature compensation gauge and calibration bars. With a complete kit, the customer can accurately monitor their bolts and determine when they need to be replaced.