Screw strength classes, product classes, clearance holes, and minimum thread engagement depths. Comprehensive guide

Understanding screw strength classes, product classifications, clearance holes, and thread engagement depths is essential for selecting appropriate fastening solutions in engineering applications. This detailed guide explores these critical aspects to enhance reliability and safety in your projects.

Screw strength classes according to DIN EN ISO 898-1 and DIN EN ISO 3506-1

Screws are classified based on their tensile strength and yield strength. For instance:

Strength Class 8.8 has a tensile strength (Rm) of 800 N/mm² and a yield strength (Re) of 640 N/mm², ideal for general structural applications.
Class 10.9 offers greater tensile strength (1000 N/mm²) and is suited for demanding structural conditions.

Product classes for screws and nuts (DIN EN ISO 4759-1)

Three product classes define tolerance and precision:

Class A: High accuracy, recommended for precise positioning.
Class B: Medium accuracy, most common in general mechanical applications.
Class C: Lower accuracy, typically for less critical assemblies.

Clearance hole diameters according to DIN EN 20273

Clearance holes ensure proper assembly without binding. For example:

For an M10 screw, precise clearance is 10.5 mm (H12), medium clearance is 11 mm (H13), and coarse clearance is 12 mm (H14).
Accurate hole selection avoids assembly difficulties and reduces material stress.

Minimum thread engagement depth for blind holes

Proper thread engagement depth is crucial for secure connections. For instance:

In materials with strength Rm = 400-600 N/mm², recommended thread depth is at least 1.2 times screw diameter for classes 4.8 to 6.8, and 1.5 times screw diameter for class 8.8.
Cast iron or aluminum alloys may require deeper threads (up to 2 times the diameter) to ensure connection integrity.

Why choosing the correct parameters matters?

Selecting the right screw strength class, product class, clearance hole size, and thread depth directly impacts your assembly’s safety, durability, and performance. Miscalculations can lead to equipment failure, structural weaknesses, or costly downtime.

At Marcopol, we provide comprehensive support and expert advice for all your fastening requirements. Browse our extensive product range of over 40,000 solutions and contact us today for personalized technical assistance.

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