3565 Bolt Extensometers for Proof Load Testing for Measuring Strain Ranges

The 3565 Bolt Extensometers are designed to measure small measuring strain ranges as required for proof load testing of bolts and similar applications such as yield measurement.

Epsilon has over 20 years history of service for the materials testing community and will be there to stand behind their products when the user’s critical application requires it.

Operation of these and all of Epsilon’s extensometers are verified to applicable standards such as ISO 9513 or ASTM E83 using in-house calibration systems. The systems are calibrated with Epsilon’s laser interferometer system.

Epsilon offers 36 Extensometer Models in numerous variations and their focus of helping customers has led to the development of models to cover virtually any test method.

The Model 3565 Extensometer uses hard conical points to contact the bolt at the center of the head and at the bottom. It is totally adjustable for varying length bolts ranging from 25 mm (1”) in length to 150 mm (6”) standard. Extension beams are offered for longer bolts.

The standard maximum measuring range is 1.25 mm (0.05”). Generally, on longer bolts this extensometer is self-supported without needing any punch marks or centering marks on the bolt. However, in the case of shorter bolts, these marks may be needed. If the conical pins are sharp, marks are frequently not needed even on the shortest bolts.

The 3565 Bolt Extensometers has a zero adjustment screw to adjust the length between the contact pins. This is used to fix the output voltage to zero, which corresponds to the exact starting position for the test. A breakaway lower arm is also included.

If a bolt fails, the breakaway arm snaps free, helping to prevent damage to the extensometer. This can be easily re-installed. If bolt failures are expected during a test, it is recommended that the user attach a cord around the upper part of the beam and tie the other end to the test frame to stop the extensometer from falling. The conical point contacts provided with the extensometer are produced using tungsten carbide.

The 3565 extensometers are strain gaged devices, making them compatible with all electronics designed for strain gaged transducers. Often they are connected to a test machine controller. The signal conditioning electronics for the extensometer is usually included with the test machine controller or may often be added.

In this case, the extensometer is supplied with the correct connector and wiring to plug directly into the electronics. Epsilon can provide many solutions if systems lack the required electronics, enabling the extensometer output to be connected to chart recorders, data acquisition boards, or other equipment.


The key features of the 3565 Bolt Extensometers are given below:

  • Full bridge, 350 ohm strain gaged design for compatibility with almost any test system
  • Standard units possess linearity readings of 0.20% or better
  • Rugged, dual flexure design for better performance
  • High quality foam lined case is provided
  • Breakaway arm to help avoid extensometer damage in case of bolt failure
  • Self-supporting on the bolt specimen usually without the need for centering or punch marks


The key specifications of the 3565 Bolt Extensometers are given below:

  • Output: 2 to 4 mV/V, nominal, depending on model
  • Excitation: 5 to 10 VDC recommended, 12 VDC or VAC max.
  • Linearity: ≤0.20% of full scale measuring range, depending on model
  • Cable: Integral, ultra-flexible cable, 2.5 m (8 ft) standard
  • Temperature range: Standard (-ST) is -40 °C to +100 °C (-40 °F to 210 °F)


The following are the options available with the 3565 Bolt Extensometers:

  • Connectors to interface to nearly any brand test equipment
  • Gauge length extension adapters
  • Shunt calibration

3565 Bolt Extensometers for Proof Load Testing for Measuring Strain Ranges


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