Concept Guide

Bolts

What a bolt is, how it differs from a screw, and the bolt types and bolt standards this library covers — hexagon head and socket head, full thread and partial thread, metric and imperial.

What a bolt is

The general case, before any specific standard is chosen.

A bolt is a threaded fastener with an external thread and a formed head, used to clamp two or more parts together. In practice the word is used for the whole family of headed, externally threaded fasteners — hexagon head bolts, socket head cap screws, and their variants.

Two things always have to be fixed before a bolt is a known part: the standard (which sets head geometry, thread and tolerances) and the size plus property class (which set the load it can carry).

Bolt or screw

The distinction is about how the joint is closed, not about the head shape alone.

	Bolt	Screw
Assembly	Passes through the parts and is closed by a nut	Threads into a tapped hole in one of the parts
Typical head	Hexagon head, driven by a wrench or socket	Socket head, driven by an internal hex key
In this library	ASME B18.2.1, DIN 931, DIN 933, ISO 4014, ISO 4017	ASME B18.3, DIN 912, ISO 4762

The boundary is not absolute — socket head cap screws are commonly used with a nut, and hexagon head bolts can be threaded into a tapped hole. Both families are covered here.

Bolt types in this library

Four families, covering the full-thread / partial-thread and metric / imperial split.

Full thread

DIN 933 / ISO 4017

Full Thread Hexagon Head Bolt · M6 - M64

Partial thread

DIN 931 / ISO 4014

Partial Thread Hexagon Head Bolt · M6 - M64

Socket head

DIN 912 / ISO 4762

Socket Head Cap Screw · internal hex drive

Imperial

ASME B18.2.1

Hexagon Head Bolt · UNC thread

Hexagon head bolts: full thread or partial thread

The most common choice in this library, and the one that most often decides the standard number.

Standard	Thread	Equivalent	Sizes	Size count
DIN 933	full thread	ISO 4017	M6 - M64	22
DIN 931	partial thread	ISO 4014	M6 - M64	17
ISO 4017	full thread	DIN 933	M6 - M64	22
ISO 4014	partial thread	DIN 931	M6 - M64	17

Full thread suits shorter grip lengths and where thread bearing is wanted. Partial thread keeps an unthreaded shank in the shear plane and suits longer grip lengths. The two are recorded as a variant pair in this library. How the DIN, ISO and ASME bolt standards line up against each other is mapped in Engineering Center.

Socket head cap screws

A separate family in this library, driven by an internal hex key.

Standard	System	Drive	Sizes
ASME B18.3	Imperial	internal hex (socket)	—
DIN 912	Metric	internal hex (socket)	M6 - M6
ISO 4762	Metric	internal hex (socket)	M6 - M6

Socket head cap screws are recorded under a separate category in this library, so their dimensional data lives on their own standard pages rather than being restated here.

Strength classes available for bolts

The property classes recorded for bolt families in this library's data source.

Property class	Typical steel	Where in this library
4.6	carbon steel	4.6
5.6 / 5.8	carbon steel	5.6 · 5.8
8.8	carbon steel	8.8
10.9	alloy steel	10.9
12.9	alloy steel	12.9
A2-70 / A4-70 / A4-80	stainless steel (A2 = 304, A4 = 316 family)	Fastener Materials
Grade 5 / Grade 8	imperial steel grades (ASME)	Fastener Materials

Property classes listed above are the ones actually recorded against bolt records in this library's data source. Strength values are on the linked pages.

Metric and imperial bolts

System	Bolts	Sizes
Metric	DIN 931, DIN 933, ISO 4014, ISO 4017	M6 – M64 for hexagon head
Imperial	ASME B18.2.1	inch sizes, UNC thread