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- Definition and Types:
- Spiral Grooves: Threads are the spiral grooves found on screws, bolts, or nuts. These grooves allow the fastener to be driven into or onto a surface, creating a secure hold.
- Helical Groove: Threads can also refer to the helical groove inside a cylindrical hole, such as in a nut, which is formed using a tap or lathe tool. This is known as a female or internal thread.
- Thread Classes:
- Class 1 Threads: Loose tolerance threads that are easy to assemble but may have more play or movement between mating parts.
- Class 2 Threads: These are the most common and are used in 90% of stainless fasteners. They have normal commercial tolerance and are found in many everyday applications.
- Class 3 Threads: These threads have stricter tolerance and provide a tighter fit, often used in applications requiring precision, such as socket cap and set screws.
- Thread Identification:
- External Threads (A): Symbolized by ‘A’ (e.g., 2A), these are threads on the outside of a fastener, such as on screws.
- Internal Threads (B): Symbolized by ‘B’ (e.g., 2B), these are threads on the inside of a fastener, such as inside nuts.
- Coarse vs. Fine Threads:
- Coarse Threads: These threads are deeper and have fewer threads per inch compared to fine threads. Coarse threads are predominant in hex head cap screws and hex nuts sold in 18-8 stainless steel, comprising 90-95% of these products and about 98% of other stainless items including machine screws and socket products. They offer advantages like greater resistance to thread stripping, better tapping in brittle materials, and improved fatigue resistance.
- Fine Threads: These have more threads per inch and a shallower depth compared to coarse threads. Fine threads are preferred for applications that require a better fit in thin-walled materials, higher torque strength, and increased tightness under vibration conditions.
- Application Considerations:
- Material Suitability: Coarse threads are often better suited for brittle materials due to their deeper grooves, which provide a more secure grip and reduce the likelihood of stripping.
- Vibration Resistance: Fine threads are typically used in applications where vibration is a concern because their higher number of threads per inch provides a more secure and tight fit.
- Torque Strength: Fine threads can handle higher torque levels, making them ideal for precision applications where exact tension is critical.
- Fatigue Resistance: Coarse threads offer better fatigue resistance, making them suitable for dynamic applications where the fastener might experience repeated loading and unloading cycles.
- Popular Sizes:
- 10/32 Diameter: This size is extremely popular and often used in a variety of applications.
Understanding the differences between thread types and their respective classes is crucial for selecting the appropriate fastener for a given application. Each type of thread has its unique advantages and is suited to specific conditions and materials.
See Related Terms:
- American Standard Pipe Thread
- Bastard Thread
- British Standard Pipe Thread
- British Standard Brass Thread
- Buttressed thread
- Chasing threads
- Class A thread
- Class B thread
- Class of thread
- Coarse thread
- Cut thread
- Depth of thread
- External thread
- Female thread
- Incomplete thread
- Internal thread
- Left-hand thread
- Male thread
- Mating thread
- Metric thread
- National coarse thread
- National fine thread
- Nut thread
- Reverse Thread
- right-hand thread
- Rolled thread
- Total Thread
- UNC thread
- UNF thread
- V-thread