Types of Nut and Bolt – Head Shapes, Thread Types & Material Grades
Types of Nut and Bolt – Head Shapes, Thread Types & Material Grades
In mechanical assembly and structural construction, selecting the right type of nut and bolt is critical for joint strength, safety, and functionality. From hex bolts used in steel structures to socket head bolts in machines, each fastener type serves a specific purpose.
This guide covers all major nut and bolt types by head shape, threading style, material grade, and application. Whether you're sourcing fasteners or designing components, this will help you identify and choose the correct combination.
Common Types of Bolts by Head Shape
| Bolt Type | Description | Common Use |
|---|---|---|
| Hex Bolt | Six-sided head, most common industrial bolt | Structural steel, machinery |
| Socket Head Bolt | Cylindrical head with internal Allen key drive | Machine parts, compact spaces |
| Carriage Bolt | Rounded head with square neck below | Wood connections, aesthetic installs |
| Eye Bolt | Loop at the head for lifting or suspension | Lifting lugs, rigging |
| U Bolt | U-shaped with two threads | Piping, cable clamping |
| Anchor Bolt | Fixed into concrete with hook or plate end | Foundation and column base plates |
Types of Nuts by Design
- Hex Nut: Six-sided standard nut used with hex bolts
- Flange Nut: Built-in washer base for better grip
- Wing Nut: Hand-tightened with two protrusions
- Lock Nut: Features nylon insert or deformed threads to resist loosening
- Dome (Cap) Nut: Closed-end nut to cover exposed threads
- Square Nut: Four-sided; used in older equipment or aesthetic projects
Bolt Thread Types
| Thread Type | Description | Use Case |
|---|---|---|
| Metric Thread | Standard ISO thread in mm (M8, M10, etc.) | All modern industrial applications |
| Unified Thread (UNC/UNF) | Used in USA, with inch-based dimensions | Imports, aerospace, older American machinery |
| Left-Hand Thread | Reverse thread (unscrews clockwise) | Rotational motion systems, heavy shafts |
| Fine Thread | Higher number of threads per length | High-precision and vibration-prone applications |
Bolt Grades and Strength Classification
Grades determine the tensile strength of bolts and should be selected based on load requirement:
- Grade 4.6: General purpose low-carbon steel bolt
- Grade 8.8: High tensile bolt for structural joints
- Grade 10.9: Higher strength, often used in automotive and heavy engineering
- Grade 12.9: Alloy steel bolt for maximum load-bearing
Material Options: MS (Mild Steel), SS 304/316, Alloy Steel, Brass, Hot Dip Galvanized, Zinc Plated
Common Nut and Bolt Sets
- M6 x 30 mm Bolt + M6 Nut
- M10 x 60 mm Bolt + M10 Flange Nut
- M16 x 100 mm Hex Bolt + Nylock Nut
- M20 x 150 mm Anchor Bolt + Dome Nut
Always select the nut thread pitch and diameter matching the bolt for proper torque and load-bearing performance.
Related Articles
- Nut Bolt Weight Chart in KG – PDF Download
- Nut Bolt HSN Code – MS, SS, Studs
- Nut and Bolt Sizes – Metric Chart
- Industrial Nuts and Bolts – Full Pillar Guide
Contact Udhhyog – Industrial Fastener Supplier
Looking for a reliable source for all types of nuts and bolts? Udhhyog offers hex bolts, structural bolts, anchor bolts, nuts, and washers in MS and SS grades across India with testing and certification.
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