ISO 7991 Low Head Screw
Low head Allen screw with hex socket, designed for industrial assemblies where available height is limited and a precise, compact and reliable fastening solution is required.
What is an ISO 7991 low head screw?
The ISO 7991 low head screw is a fastening solution used in mechanical assemblies where there is not enough space for a standard cylindrical head, or where the external volume of the joint needs to be reduced.
Its hex socket drive allows clean and precise installation, while maintaining a compact geometry suitable for machinery, fixtures, technical plates and assemblies with height restrictions.
Low head
Reduces the visible height of the screw and allows more compact assemblies.
Hex socket
Enables tightening with an Allen key or controlled hexagonal tool.
Technical design
Suitable for applications where space, precision and integration matter.
Main technical characteristics
When should a low head screw be used?
Height restriction
When a conventional cylindrical head protrudes too much or interferes with other parts of the assembly.
Compact design
Ideal for systems where every millimetre matters and the fastening must be integrated into the mechanical design.
Clean assembly
Provides a more orderly technical appearance on plates, covers, fixtures and visible subassemblies.
Allen key access
The hex socket makes installation easier in areas where an external wrench would not have enough space.
Common materials and finishes
Carbon steel
- 8.8 · general industrial use
- 10.9 · higher mechanical strength
- 12.9 · demanding applications
Stainless steel
- A2 · standard environments
- A4 · humid or corrosive environments
- Specials · according to drawing or technical requirement
Material selection must be based on load, working environment, corrosion resistance, temperature and traceability requirements.
Technical parameters to review
| Parameter | Description | Technical importance |
|---|---|---|
| Nominal diameter | Screw metric size | Defines load capacity and thread compatibility |
| Thread pitch | Distance between threads | Must match the female thread or insert used |
| Head height | Reduced profile | Key in applications with limited space |
| Hex socket | Allen key recess | Allows tightening torque to be applied with the correct tool |
| Total length | Measured under head or according to specification | Must adapt to the thickness of the assembled components |
| Material | Steel, stainless steel or special alloy | Determines strength, durability and service performance |
Comparison with other Allen screws
Low head
- Reduced profile
- Compact assembly
- Good visual integration
- Use in limited spaces
Cylindrical head
- Greater head height
- General mechanical use
- Good tightening capacity
- Higher external volume
Button head
- Rounded finish
- Functional low profile
- Use in covers and casings
- Visible technical aesthetics
Common industrial applications
Assembly recommendations
Check available height
Before selecting the screw, check the free distance above the part to avoid interference with other elements.
Use the correct tool
The hex socket must be driven with the proper tool to avoid damaging the recess during tightening.
Control tightening torque
With reduced-profile heads, excessive tightening should be avoided to prevent deformation of the head or compromise of the fastening.
Manufacturing of standardized and special screws
At AREM-CNC, we manufacture machined components according to drawing or technical standard, with certified materials, dimensional control and full traceability.