Screws – Overview of standard

There are different designation systems for the properties of screws. The underlying standards form the basis for classifying and designating screw types. This article briefly presents some of the different screw standards and their differences, and provides a general overview of screws in the European region.

Overview of screw standards

Standards are used for standardization and represent an agreement within a specific group that has agreed on this standard. Since many national standards have emerged over time and under the influence of historical and regional developments, they are often only commonly used and recognized in these regions. Worldwide, there are a variety of standards to ensure that screws meet specific requirements. The use of, and compliance with, standards is generally not binding, but can be contractually agreed or mandated by lawmakers. These standards are essential to ensure the quality, safety and functionality of fasteners.

Standards

The Deutsche Institut für Normung e.V., abbreviated as DIN, is responsible for determining and updating the national DIN standards. Standardization in the European single market are aimed at European standards, abbreviated as EN. EN standards will be adopted into national standards as quickly as possible and without changes after the resolution of the European Council; in Germany they are called DIN EN. The corresponding DIN is withdrawn and replaced by the DIN EN. ISO standards are intended to facilitate worldwide standardization. Global ISO standards should categorically be adopted into EN standards without changes. As a global manufacturer with headquarters in Japan, MISUMI also produces and sells products that are standardized iaw. the national standard JIS (Japanese Industrial Standard). The respective standard describes the details of standardized screws, including diameter, (thread) length and head shape.

The following explains the screw designation iaw. DIN:

• DIN 933 M 10 x 80 A2-70

The abbreviation DIN 933 stands for hex screws with thread up to the head. M10 x 80 refers to a 10 mm (M10) diameter metric screw with a 80 mm length. A2-70 describes a stainless steel specification that not only indicates the quality and corrosion resistance of the material, but also a minimum tensile strength of 700 N/mm². In addition to this information, the respective standards generally contain the relevant thread tables.

DIN screws

DIN standards are best known in Germany. In the past, many screws have already been standardized in Germany using a DIN standard. For example, DIN 933 applied to hex screws. The aim of establishing global standards has led to the development of international standards (ISO standards) for a growing number of applications and to the replacement of DIN standards with corresponding EN standards or ISO standards. Nevertheless, DIN standards apply whenever there is no corresponding successor standard as DIN EN or ISO standard (DIN EN ISO).

ISO screws

ISO regulates various screw standards at an international level. Many ISO standards largely contain the same regulations as the previously valid DIN standards. However, they are used in several countries. The successor standards for DIN 931 and DIN 933 are, for example, DIN EN ISO 4014 and DIN EN ISO 4017. Other standards are:

• ISO 4762 for socket head cap screws with hex socket
• ISO 7380 for flat head screws with hex socket
• ISO 2009 for countersunk screws with slot
• ISO 7045 for pan head screws with Phillips cross slot
• ISO 965 for general-purpose threads

In mechanical engineering, hexagon head screws in accordance with DIN EN ISO 4014 and cylinder screws in accordance with DIN EN ISO 4762 are most commonly used.

Screws iaw. JIS

The Japanese Industrial Standard (JIS) standard is published by the Japanese Standards Association. Many screws are also standardized in the metric unit system. In addition to various overlaps of screws that are standardized iaw. the Japanese JIS standard with those that were manufactured iaw. DIN or ISO, there are sometimes significant differences in certain screw types. In some cases, special tools are required for the JIS standard.

Common JIS standards for threads include:

• JIS B 0205-1:2001 for general metric thread (standard angle shape)
• JIS B 0205-2:2001 and JIS B 0205-3:2001 for general-purpose metric threads
• JIS B 0205-4:2001 for general metric thread (standard dimensions)
• JIS B 0207:1982 for metric fine threads

MISUMI offers screws of all standards.

Meaning of the differences

Differences in standardization primarily affect the choice of tools. As a rule, JIS screws are compatible with tools that are adapted to DIN screws. Nevertheless, the so-called cam-out effect (tool slipping out of the screw head) can occur, for example, on Phillips screws iaw. the JIS standard when using unsuitable tools. It is therefore recommended to use special JIS tools for JIS screws. This maintains ease of movement and screws are not unnecessarily damaged.

Thread types and their differences

A thread is a helical elevation or recess on a screw, a bolt or another fastening element. The threads are also subject to the standards. The following parameters describe the threads in more detail:

• Thread tips: are the outer edges of a thread.
• Outer diameter: also called nominal diameter, is the diameter of the outer threaded part. Thread-outer diameter tables are used to determine the required outer dimension.
• Core diameter: also called core hole diameter. When cutting threads, a core hole bore ensures correct centering. The core hole determines the smallest inner diameter of the subsequent thread. There are various threaded core hole tables for reading the associated nominal dimensions and pitches.
• Edges: ae the oblique or inclined sides of a thread that form the helical elevations or recesses and extend along the thread profile.
• Pitch: the thread pitch is a dimension that indicates the distance between successive threads or elevations of a thread. It is defined differently depending on the thread. For metric threads, the thread pitch results, for example, from the path traveled in one revolution. For inch threads, for example, the thread pitch is determined by the number of threads per inch.
• Pitch angle: the pitch angle is the angle at which the thread flanks of a thread rise or fall (as seen along the thread profile).
• Start: is the continuous recess in the helix (around or in a bolt/nut).

Thread shapes are different worldwide and often lead to challenges in the compatibility of screws and their applications. Germany and many other European countries primarily use metric threads, which are characterized by a standardized pitch and angle. This standardization facilitates identification and application. In contrast, the USA traditionally uses inch threads. In the USA, Unified Thread Standard (UTS) threads are particularly common, which differ significantly in their classification and dimensions from the metric systems. In Japan, the metric system for threaded connections is widely used. For pipe threads, inch threads are typically used internationally for all standardization regions. The different thread pitches, angles and dimension systems (metric vs. inch) have the effect that the usability of screws from different regions is often limited or not possible at all. Due to the historical development of thread standards worldwide, it is essential to precisely check the thread before using screws. This prevents damage and ensures the functionality of connections.

Different screw head types

In addition to the actual thread, the heads of the screws also play an important role. Various screw heads and their advantages are presented below:

Round head

Round head screws have a round head that extends beyond the surface of the material into which they are screwed. The head can be either completely round or slightly hemispherical, depending on the design. The round shape reduces the risk of injury, offers a larger contact surface and allows for uniform load distribution.

Cylinder head

The cylinder head is a flat screw head with a cylindrical surface. It is threaded in from above, which is why it is suited for use in difficult-to-reach areas. DIN standards 4762 and 912 or JIS B 1176 apply for hexagon socket head cap screws. Flat head screws are a special shape of cylinder head screws.

Hexagon head

The hexagon head has six sides and a flat surface with six corners. It is easy to grasp and tighten with a hex wrench or an open-face wrench. Hexagon head screws are suitable for high torque applications. Unlike round head screws driven from the inside, a hexagon head screw is tightened with the force that acts on the head from the outside. DIN standards 4014 and 933 or JIS B 1180 apply to hexagon head screws.

Countersunk head

Countersunk screws have a tapered screw head that allows the screw to be countersunk into the material. They are often used when the screw head needs to be flush with the surface of the material to provide a smooth surface without protruding parts. Countersunk screws reduce the risk of tripping and injury. DIN ISO 10642, for example, applies for countersunk screws.

Pan head

Pan head screws have a semicircular head. This head distributes the load evenly over the total surface area and stresses the material less. Penetration of the screw head into the workpiece is avoided, the service life is extended. DIN ISO 7380-2, for example, applies for pan head screws.

Knurled screw

Knurled screws are characterized by a head with a knurled surface that provides increased grip. This special texture makes it possible to tighten or loosen the screw by hand without tools. Knurled screws are particularly suitable for applications that require frequent manual adjustment or for areas where quick access without tools is important, such as on housings for electronic equipment or adjustment mechanisms.

Wing head

Wing screws have two lateral, wing-like protrusions that allow easy tightening and loosening by hand without tools. This screw head is particularly useful for applications that require quick and frequent adjustment, e.g. when attaching to machine covers or when adjusting various equipment. The wide wings offer good handling with corresponding leverage effect, which facilitates tightening and loosening, even if greater forces are required.

Eye bolts

Eye bolts, also called ring bolts, are characterized by a circular ring that looks like an "eye" on the head. This design allows hooks to be engaged or cables to be threaded through, thus supporting a variety of mounting and lifting tasks. They are particularly useful for applications that require suspension, such as transporting heavy loads. Eye bolts provide a secure attachment point and are designed to function reliably even under heavy loads. Thanks to their robust construction, they can withstand tensile and also shear forces.

Other head shapes

In addition to the classic head shapes, such as round, cylinder and hexagon head screws, there are also less common, but nevertheless important, head shapes such as square and triangular screw heads. Square head bolts offer high resistance to twisting and are particularly popular in the assembly industry, which requires robust connections. Triangular screws, which require special tools for tightening, offer additional security against unauthorized unthreading and are therefore often used in safety devices. Technological advances and increasingly specific requirements of various industries have led to the development of additional screw head shapes that can offer optimized solutions for special assembly or safety requirements.

Various screw drives

Choosing the right screw drive is crucial for efficient and safe assembly operations. The most common types are slotted screws, Phillips screws, socket head cap screws, and external hex screws. Slotted screws are one of the oldest screw shapes and are often used for simple applications that do not require high torque. Phillips screws provide better support and are often used in electrical engineering and in general mechanical engineering. Hex cap screws, also known as Allen screws, provide even greater torque transfer and are often used for connections requiring high strength. External hex screws, on the other hand, are ideal for applications that use wrenches and require higher torque. Each screw connection requires specially shaped tools that are precisely matched to the fit and shape of the screw connection in order to ensure optimal support and optimal torque transfer. For example, hexagon socket and Torx drives require wrenches or bits that fit into the screw profile and prevent head damage. These tools are available in metric and inch systems, making them easy to use in various regions and industries. When using JIS screw drives, it is recommended to order a special JIS screwdriving tool.

Overview of screw standards

Without claiming to be complete, the following table shows the various screw standards: