Screw heads and drive types: what withstands industrial torque? With torque table and failure mode analysis

In industrial applications it is easy to assume that all screws perform in the same way. But when high torque and continuous loading enter the picture, the differences become clear. The screw head determines how efficiently force is transferred from tool to fastener, how well the grip is maintained during tightening, and whether the connection maintains a stable preload over time.

In sectors such as oil and gas, offshore, mining and heavy industry, fasteners are exposed to constant vibration and varying loads. The wrong drive type can lead to slipping (cam-out), deformation of the screw head and failure to reach the specified torque.

Overview: drive types for industrial applications

Hex screws — robust and versatile

Hex screws (DIN 933 and DIN 931) have an external hexagonal head that provides stable contact between tool and screw. This design makes it possible to transfer high torque without losing grip, while the load is distributed evenly across several faces. That is why this is one of the most widely used solutions in structures, flange connections and general industrial assembly.

The hex head contacts the tool across 6 faces, and the typical torque transfer capacity is limited by the tensile strength of the bolt itself — not by the ability of the head to transfer force. This makes hex the standard choice for large dimensions (M16 and up) where torque requirements are high.

Failure mode: using the wrong tool size or worn tools can round off the hex head. The correct wrench size and calibrated torque wrenches eliminate this.

Unbrako (internal hexagon) — precision in tight spaces

Unbrako screws (DIN 912, cylinder head with internal hexagon) give a deeper and more controlled engagement between tool and screw than an external hexagon of the same size. This gives better control during tightening and reduces the risk of damage to the screw head, even under high load.

They are often used in applications where space is limited or where precision is required — for example machine components, moulds and compact systems. The internal hexagon also gives controlled access where an external wrench cannot reach.

Failure mode: the recess rounds off when a worn tool or the wrong size is used. Requires the correct hexagon bit and regular tool checks.

Torx — maximum torque transfer

Torx screws (ISO 10664) are designed to handle high torque more efficiently than traditional drive types. The star-shaped geometry with 6 lobes gives more contact points and distributes the load more evenly between tool and screw.

Practical benefit: Torx transfers 30–40% more torque than hex at the same size before there is any risk of tool slip or head deformation. This gives a more stable installation process, less tool wear and higher repeatability — particularly important in production environments.

Torx is available in sizes T6 to T100, where the number refers to the size of the drive (not the screw diameter). Common industrial sizes: T20, T25, T30, T40, T50.

Why Phillips and Pozidriv are not suitable for industrial assembly

Phillips (PH) was developed for simpler assembly work, not for high industrial torque. The geometry is deliberately designed so that the tool loses its grip (cam-out) when the load becomes too high — this protects the screw head against over-tightening in light assembly, but is problematic in applications where the correct torque must be achieved.

Pozidriv (PZ) is a further development of Phillips with additional ribs that delay cam-out, but the principle is the same. In practice this means that the correct torque is not achieved, while the screw head may also be damaged. Over time this reduces the preload and increases the risk of failure.

These drive types are therefore not used in applications where strength and operational reliability are required. They have their place in light-torque assembly work, but not in structural or dynamically loaded fasteners.

Decision matrix: which drive type should you choose?

The drive type is only half the story — the locking method is the other

In connections exposed to vibration, the choice of drive type is only half the story — the locking method is the other half. Traditional lock washers rely on friction, and friction decreases under settling and cyclic loading.

The Nord-Lock wedge principle (wedge-locking) secures the preload through geometric tension locking — independent of the friction in the thread. Two washers with wedge-shaped undersides clamp in a way that counteracts the tendency of the bolt to loosen under vibration. INDUSTRISALG holds a wide range of Nord-Lock wedge washers in stock.

For applications with ATEX classification, high-frequency vibration or documented preload loss in a previous installation, the combination of the correct drive type + a Nord-Lock wedge washer is the solution we recommend.

Frequently asked questions

What is the difference between Torx and Unbrako?

Unbrako uses an internal hexagon (6 flat sides). Torx uses a 6-lobed star shape with more contact points. Torx transfers 30–40% more torque at the same size and gives lower tool wear. Unbrako is less expensive and widely available.

Which DIN standard applies to hex screws?

DIN 933 covers hexagon bolts threaded all the way (fully threaded). DIN 931 covers hexagon bolts with a shank (partially threaded). The ISO equivalents are ISO 4017 and ISO 4014.

What is cam-out?

Cam-out is the phenomenon where the tool slips out of the screw head during tightening. Phillips drivers are designed to do this under overload, as protection against over-tightening. In industrial applications it is undesirable because it prevents the correct torque from being achieved.

Can I use Torx in all dimensions?

Torx is typically available for screws from M2 to M16. For larger dimensions (M20+), hex or Unbrako is more practical. Torx is particularly suited to small and medium dimensions where the torque requirement is high and tool wear is a factor.

Conclusion

In industrial applications where high torque is a factor, the choice of drive type is decisive for both performance and safety. Hex screws, Unbrako screws and Torx screws give the strength and control required to secure stable connections over time. Other solutions such as Phillips and Pozidriv were not developed for such loads and will therefore not deliver the same level of reliability.

The correct choice of screw head — combined with a Nord-Lock wedge washer where vibration is a factor — contributes to reduced maintenance, fewer failures and lower total costs. INDUSTRISALG stocks hex, Unbrako and Torx in M3–M48 in strength classes 8.8/10.9/12.9, as well as a full range of Nord-Lock wedge washers.

Related reading

• Standardized product range: why fewer variants reduce total costs
• Measuring screw length: the most common mistakes and costly consequences

Get in touch

If you are unsure which combination of drive type and locking solution suits your application, we can help you assess the requirements for torque, environment and load — and confirm stock status for both screws and Nord-Lock wedge washers the same day.