DIN (German Institute for Standardization) and ISO (International Organization for Standardization) numbers on a tool mean it's built to a published, testable specification — dimensions, hardness, torque capacity.
Common ones on Teng tools
DIN 3113A — combination wrenches: head geometry and strength.
DIN ISO 1711-1 — assembly tools for screws and nuts.
ISO 6789 — torque wrenches: accuracy and testing. Every Teng torque wrench is individually tested and supplied with a Declaration of Conformance.
If a spec matters for your compliance paperwork (aviation, defense, institutional buyers): Teng Tools USA is TAA approved and our torque tools ship with conformance documentation. Ask us if you need certificates.