ISO 898-2 Test force test on nuts DIN EN ISO 898-2
DIN EN ISO 898-2 specifies the mechanical properties of nuts made of carbon or alloy steel with metric ISO thread fixed. The focus is on the so-called Test force test, which proves that a nut can withstand a defined axial load without showing failure or thread damage.
The standard is a supplement to ISO 898-1 (screws) and ensures that both components of a screw connection are mechanically matched.
Key facts at a glance
DIN EN ISO 898-2 defines the minimum test forces for nuts of certain strength classes and describes the method used to verify these forces. Unlike bolts, the focus here is not on determining tensile properties, but on verifying that the The nut remains functional under a defined axial load.The test is usually carried out as a pressure or test force test and, if the product behaves according to standards, is considered practically non-destructive.
Key points:
- Scope: Nuts with metric ISO thread
- Proof of test force FP (Force Proof)
- Holding time of the test force at least 15 seconds
- No stripping or thread failure permitted
- Supplement to ISO 898-1 (screws)
What does DIN EN ISO 898-2 regulate?
DIN EN ISO 898-2 specifies the mechanical properties of nuts used with bolts according to ISO 898-1. It defines strength classes for nuts and assigns a minimum proof load (FP) to each.
The goal is to ensure that the nut, under axial load:
- did not fail plastically,
- shows no thread tear-out
- and remains functional after the stress.
The standard applies to nuts with metric ISO threads and defines the required test conditions depending on the nominal diameter and strength class.
The test force test according to DIN EN ISO 898-2
Test principle
The nut is screwed onto a hardened test mandrel with a defined thread. An axially acting force is then applied, corresponding to the test force specified for this size and strength class.
The examiner will be:
- built up with a defined ramp time (often 10 seconds),
- held for at least 15 seconds
- subsequently completely relieved.
If the mother passes the test, she is allowed to:
- not stripped from the test mandrel,
- show no visible thread damage,
- It should be removable without tools after the first turn.
Non-destructive nature of the test
If the nut meets the normative requirements, the test is practically non-destructive. The nut remains functional and shows no permanent damage.
Tensile test in arbitration proceedings
The test is usually carried out as a pressure or test force test.
In the event of arbitration – for example, in the case of disagreements between supplier and customer – a tensile test can alternatively be carried out. This serves to clearly clarify the mechanical performance.
Test personnel and machine selection
DIN EN ISO 898 specifies test force values up to 600 kN. Therefore, in industrial practice, a universal testing machine with a maximum test force of 600 kN is frequently used.
For nominal forces above 600 kN, the standard alternatively allows a hardness test.
Important for machine selection:
- sufficient test force range
- stable and rigid frame construction
- precise force control
- reproducible holding times
- Calibration of force measurement according to ISO 7500-1
In this experiment, the machine primarily serves to apply and maintain the test force in a controlled manner. The recorded force-time diagram is mainly for documentation purposes.
Typical experimental procedure
A standardized process might look like this:
- Selection of the target force FP (e.g. M16 – defined test force in Newtons)
- Setting the ramp duration (standard is often 10 seconds)
- Setting the holding time (minimum 15 seconds)
- Inserting the test mandrel with the nut screwed on.
- Automatic approach to the starting position
- Start of the testing process
- Relief after the holding period has expired
- Loosening and visual inspection of the nut
Requirements for testing machines according to ISO 898-2
Universal or pressure testing machines with suitable force control are suitable for carrying out the test force test.
The decisive factors are:
- precise and stable force control
- secure holding function for at least 15 seconds
- reproducible ramp control
- Documentable force-time recording
- Calibration according to ISO 7500-1
Special test mandrels and clamping systems ensure a centric force transmission and prevent off-center loads.
FAQ on ISO 898-2
What is the difference between ISO 898-2 and ISO 898-1?
ISO 898-1 regulates the mechanical properties of screws and determines them via the tensile test, in which characteristic values such as tensile strength and yield strength are determined.
ISO 898-2, on the other hand, refers to nuts and does not prescribe a classic tensile test, but rather a load test. This test verifies that the nut can withstand a defined axial load without the thread failing or the nut undergoing plastic deformation.
The two standards complement each other: only the standard-compliant interaction of screw (ISO 898-1) and nut (ISO 898-2) ensures the mechanical performance of the entire connection.
Is the test according to ISO 898-2 destructive?
No. If the nut meets the required quality standards, the test load test is practically non-destructive.
Why isn't a classic tensile test being performed?
The standard primarily defines the load test for nuts, as this focuses on the thread behavior under axial load. The tensile test is only used in the event of an arbitration dispute.
What happens if something fails?
If the nut shows thread tearing, stripping or permanent damage, the test is considered failed.
