Torque explainer: why ISO 6789 splits design from calibration

The 2017 revision of ISO 6789 did something quietly important for torque tools: it split the standard in two. Part 1 covers design conformance and quality testing — what the manufacturer proves about a model of wrench. Part 2 covers calibration proper, with a full measurement-uncertainty treatment for the individual tool on the bench.

The split matters because the two questions get conflated in purchasing and audits. A tool 'complying with ISO 6789' out of the box has passed a type test; it says little about THIS wrench after a year on your line. Conversely, a calibration to Part 2 with stated uncertainty tells you about this wrench today — and nothing about how long it stays true.

That second question — how long — is interval analysis, and ILAC-G24's methods (reliability targets, as-found data, adjustment rules) apply to click wrenches exactly as they do to gauge blocks. The community Q&A thread on torque intervals walks a worked version of that reasoning.