12.9 Grade – White zinc – Hexagon bolt

Grade 12.9 Technical Overview

Grade 12.9 bolts are strictly for engineering scenarios where failure is not an option. They offer a tensile strength that is 50% higher than Grade 8.8 and 20% higher than Grade 10.9. However, this extreme strength comes with a trade-off: increased hardness means reduced ductility. Therefore, these bolts should be used in rigid connections where shock loading is minimized.

Mechanical Properties Specification

The "12.9" designation on the bolt head conveys the following critical data according to ISO 898-1:

Property	Value	Implication
Tensile Strength	1200 N/mm² (Min)	Offers the highest resistance to snapping under tension.
Yield Strength	1080 N/mm² (Min)	90% of tensile strength. Allows for extremely high torque settings and preload.
Hardness (Rockwell C)	39-44 HRC	Very hard surface, requiring high-strength tools for installation.

Quality Assurance

For such critical components, verifying material quality is essential. We can provide an EN 10204 3.1 Material Certificate upon request to validate the alloy steel composition. Please note that third-party inspection services require an additional fee.

Advanced Industrial Applications

Grade 12.9 bolts are typically found in the heaviest and most demanding machinery:

• Hydraulics: Fastening hydraulic cylinders and pumps operating under extreme pressure.
• Forging & Stamping: Used in die-casting machines and forging presses.
• Engine Components: Connecting rods and main bearing caps in high-performance engines.
• Heavy Earthmoving: Critical pivot points on excavators and bulldozers.

Frequently Asked Questions

What is the risk of Zinc Plating on Grade 12.9 bolts?

The biggest risk is Hydrogen Embrittlement. Because Grade 12.9 steel is so hard (over 39 HRC), it is extremely sensitive to hydrogen absorbed during the acid pickling and plating process. If not properly baked immediately after plating, the bolts can suffer brittle failure (snap suddenly) under load. We ensure our plated 12.9 bolts undergo de-embrittlement treatment, but for absolute safety in critical fatigue zones, non-plated (black oxide) bolts are sometimes preferred.

Can I replace Grade 10.9 with Grade 12.9?

Technically yes, as it is stronger. However, Grade 12.9 is less ductile (less stretchy) than 10.9. In applications with heavy vibration or impact loads, a Grade 10.9 bolt might actually perform better because it can absorb some shock without cracking, whereas a 12.9 bolt might be too brittle.

Do I need special nuts for Grade 12.9 bolts?

Absolutely. You must use Class 12 high-strength nuts. If you use a standard Grade 8 nut with a Grade 12.9 bolt, the threads of the nut will strip long before you can tighten the bolt to its proper capacity, rendering the high-strength bolt useless.