Fastener Glossary
Common terms from drawings, certs and the shop floor, in plain English.
Terms
| Term | Meaning |
|---|---|
| Proof load | Test load a part must hold without permanent stretch |
| Yield strength | Stress where permanent stretch begins |
| Tensile strength | Stress at breaking |
| Preload / clamp load | Tension in a tightened bolt |
| K factor (nut factor) | Friction constant in T = K x D x F |
| Tensile stress area | Effective area used for thread strength |
| Grip | Thickness of material clamped |
| Thread engagement | Length of thread in contact |
| UNC / UNF | Unified coarse / fine inch threads |
| Class 2A / 2B | Standard inch thread fit, external / internal |
| Property class | Metric strength designation, e.g. 8.8 |
| Q&T | Quenched and tempered heat treatment |
| Hydrogen embrittlement | Delayed brittle fracture from absorbed hydrogen |
| Galling | Thread seizure, common in stainless |
| MTR / CoC | Mill test report / certificate of conformance |
| Lot traceability | Link from part to its production and test records |
Governing standards: SAE J429 (2014); ISO 898-1:2013; ASME B1.1-2023. Editions shown are the latest confirmed as of September 2026. The drawing and the governing standard always take precedence over this sheet.
These tables carry the same figures as the printed sheet below.
The printed sheet
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Text version of this sheet
Fastener glossary
FIELD IDENTIFICATION
What it is
Common terms from drawings, certs and the shop floor, in plain English.
LENGTH
HEAD
SHANK
THREAD
Parts of a fastener
Terms
Term
Meaning
Proof load
Test load a part must hold without permanent stretch
Yield strength
Stress where permanent stretch begins
Tensile strength
Stress at breaking
Preload / clamp load
Tension in a tightened bolt
K factor (nut factor)
Friction constant in T = K x D x F
Tensile stress area
Effective area used for thread strength
Grip
Thickness of material clamped
Thread engagement
Length of thread in contact
UNC / UNF
Unified coarse / fine inch threads
Class 2A / 2B
Standard inch thread fit, external / internal
Property class
Metric strength designation, e.g. 8.8
Q&T
Quenched and tempered heat treatment
Hydrogen embrittlement
Delayed brittle fracture from absorbed hydrogen
Galling
Thread seizure, common in stainless
MTR / CoC
Mill test report / certificate of conformance
Lot traceability
Link from part to its production and test records
Governing standards: SAE J429 (2014); ISO 898-1:2013; ASME B1.1-2023. Editions shown are the latest confirmed as of September 2026. The drawing and the governing standard
always take precedence over this sheet.
torquing any fastener. Verify the current governing standard, project documents, OEM requirements, size, thread, coating and lot certification. To the fullest extent permitted by law, The Fastener App disclaims liability
arising from reliance on this reference.
Fastener Guide reference FG-0DFCDA · thefastenerapp.com/fastener-guide/technical-reference/fastener-glossary · © The Fastener App. Reference only — verify the current governing standard, drawing and manufacturer data before specifying or installing.
