Epsilon MODEL 3565 Bolt Extensometers for Proof Load Testing

Epsilon Model 3565 bolt extensometers measure small measuring strain ranges in applications such as yield measurement and proof load testing of bolts.

Hard conical points are used for contacting the bolt at the center of the head and at the bottom. The extensometers are completely adjustable for bolts of different lengths, from 25mm to 150mm standard.

The standard maximum measuring range of the Epsilon model 3565 bolt extensometers is 1.25mm. In the case of testing longer bolts, this extensometer is generally self-supported and punch marks or centering marks on the bolt are not required.

However, these marks may be needed in the case of shorter bolts. If sharp conical pins are available, then these marks are often not required even on the shortest bolts.

With a zero adjustment screw, the length can be adjusted between the contact pins. With this, the output voltage can be set to zero corresponding to the correct starting position for the test.

The Model 3565 also features a breakaway lower arm, which prevents the extensometer from damage by snapping free in the event of specimen failure and is easily re-installed.

If bolt failure is unavoidable during a test, users are advised to connect a cord around the beam’s upper part and attach the other end to the test frame so that the extensometer can be prevented from falling. The extensometer also features conical points contacts made from tungsten carbide.

As strain gauged devices, the Model 3565 extensometers show compatibility with any electronics used in strain gauged transducers. They are often coupled to a test machine controller.

For these extensometers, the signal conditioning electronics are generally integrated into the test machine controller or may often be added. In this case, the unit is supplied with the appropriate connector and wiring for direct plugging into the electronics.

Epsilon also provides a range of solutions for units devoid of the required electronics, enabling connection of the extensometer output to equipment, including charter recorders and data acquisition boards.

Epsilon MODEL 3565 Bolt Extensometers for Proof Load Testing

Model 3565 Extensometers

Key Features

The key features of the Model 3565 bolt extensometers include:

  • Rugged, dual flexure design for improved performance
  • All standard units have linearity readings of 0.20% or better
  • Full bridge, 350Ω strain gauged design for compatibility with almost all test systems
  • Breakaway arm to help prevent extensometer damage in the event of bolt failure
  • Self-supporting on the bolt specimen, typically without requiring centering or punch marks
  • Includes high quality foam lined case


Options available include gauge length adapters and connectors to interface to virtually all brands of test equipment.

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