What are M20 Screws?

M20 screws are large-diameter metric fasteners featuring a 20mm thread, available in both coarse (2.5mm) and fine (1.5mm) thread pitches. Designed for structural and heavy-duty industrial use, the M20 bolt is one of the most widely specified fastener sizes in civil engineering and mechanical construction.

In steel-framed buildings, M20 bolts form the backbone of beam-to-column connections, where their load capacity and reliability are essential to structural integrity. Whether specified as an M20 cap head screw for precision-machined assemblies or an M20 socket head cap screw for applications requiring a compact head profile, this fastener size delivers the strength engineers demand.

How M20 Size Screws Work

The M20 screw is a workhorse in sectors ranging from construction and infrastructure to energy and transport. Its 20mm diameter provides a substantial cross-sectional area, translating to high tensile and shear strength across bolted joints.

M20 bolts are routinely used to secure base plates, gusset connections and flanged joints in structural steelwork, where they are tightened to precise torque values to achieve controlled preload. The fine pitch variant is particularly valued in applications requiring tighter preload control and enhanced resistance to self-loosening under vibration. In wind turbine tower assemblies, M20 cap head screws resist the cyclic fatigue loads generated by constant wind exposure. Their versatility extends from permanent structural connections through to heavy plant that requires periodic disassembly for maintenance.

Materials M20 Screws Are Made From

Our M20 screws are crafted from high-quality materials to support a variety of operational requirements:

• High-Tensile Steel: Provides exceptional strength and durability, ideal for structural bolting and applications under heavy load.
• Stainless Steel Grades A2 and A4: A2 is a versatile option for general use, while A4 offers superior resistance to corrosion, perfect for marine and chemical environments.
• A4-80 Stainless Steel: Combines the corrosion resistance of A4 with enhanced tensile strength for demanding installations.
• BUMAX Stainless Steel: High-strength stainless steel fasteners that combine corrosion resistance with mechanical performance comparable to high-tensile steel.
• Aluminium: Lightweight with good corrosion resistance, suited to applications where weight reduction is a priority.
• Titanium: Offers an outstanding strength-to-weight ratio and excellent corrosion resistance, specified in aerospace and high-performance engineering.
• Nylon and PEEK: Lightweight thermoplastics known for excellent chemical resistance and high thermal stability, often used in advanced engineering projects.

Sizes and Types of M20 Screws Available

M20 screws come in a wide range of configurations to meet various project specifications:

• Lengths: Available in lengths ranging from 20mm to 300mm.
• Head Types: Cap head, countersunk and hexagon profiles are available to suit different installation and clearance requirements.
• Thread Types: Fully threaded, partially threaded and specialised options like captive screws provide flexibility for different fastening requirements.
• Drive Types: Choose from Hex Socket and External Hex drive styles to suit your tooling preferences.
• Finishes: Options such as AccuLock thread locking prevent loosening under vibration, while AccuBlack chemical blackening delivers a sleek, dark aesthetic.

FAQs

Q: What size is an M20 bolt?

 A: An M20 bolt has a thread diameter of 20mm, available in coarse (2.5mm) and fine (1.5mm) thread pitches. Lengths vary depending on the product type; hexagon bolts, for example, are available in lengths from short through to 200mm as standard. The across-flats dimension for an M20 hex head is 30mm.

Q: What is the difference between an M20 cap screw and an M20 hex bolt?

 A: An M20 cap screw typically refers to a socket head cap screw (DIN 912) with an internal hex drive, designed for use with a hex key. An M20 hex bolt features an external hexagonal head, tightened with a spanner or socket wrench. Both share the same M20 thread, but differ in head profile, drive type and typical application.

Q: Can M20 bolts be used in structural steelwork?

 A: Yes. M20 bolts, particularly in high-tensile steel grades 8.8 and 10.9, are one of the most commonly specified sizes in structural steel connections, compliant with standards such as BS EN 15048 and BS EN 14399 for preloaded assemblies.

Q: What hex key is needed for an M20 socket cap screw?

 A: An M20 socket cap head screw (DIN 912) requires a 17mm hex key for installation and removal.

Q: Are M20 screws available with thread-locking?

 A: Yes. AccuLock pre-applied thread-locking patches are available across the M20 range, providing vibration resistance without the need for liquid threadlocker during assembly.

Bespoke M20 Screws Manufacture.

High precision, bespoke manufacture of M20 Screws to customer specification. State of the art facilities specialising in both small batch prototyping and large scale manufacture.