Metric Threads
- Format is M major diameter (mm) X pitch (mm)
- Example: M12 X 1.75 is a thread having a nominal major diameter of 12 mm and a pitch of 1.75 mm.
- The letter M is the clue to the metric designation.
- Similar classification are given for other threads
- For metric threads, pitch is the distance between threads.
- Example shown to the right
.png?version=1&modificationDate=1605696139707&cacheVersion=1&api=v2&width=200&height=180)
Unified Threads
- Dimensions specified in inches
- Coarse and fine series exist and are termed UNC and UNF respectively.
- Format is major diameter – threads per inch series
- Example: 5/8” – 18 UNF is a thread having nominal major diameter of 5/8”, 18 threads per inch, and belongs to the fine thread series.
- Screw sizes with diameter under ¼” are numbered (i.e., small screw diameters are designated by gauge sizes, and not by fractions of an inch).
- Unified threads have thread angle of 60.
Fine Threads vs. Coarse Threads
Reading Data Sheets
- Static Load Rating (always stay below) – maximum stationary load before total permanent deformation of the fastener.
- Operating Load Rating (always stay below) - maximum permissible live load before total permanent deformation of the fastener.
Standards (Page link)
- ASTM's fastener standards specify, test, and evaluate the material, dimensional, mechanical, and metallurgical properties of various fasteners. These fastener standards allow manufacturers and users to examine fasteners to ensure their strength and quality for safe utilization1.
References
Metric Threads
- Format is M major diameter (mm) X pitch (mm)
- Example: M12 X 1.75 is a thread having a nominal major diameter of 12 mm and a pitch of 1.75 mm.
- The letter M is the clue to the metric designation.
- Similar classification are given for other threads
Unified Threads
- Dimensions specified in inches
- Coarse and fine series exist and are termed UNC and UNF respectively.
- Format is major diameter – threads per inch series
- Example: 5/8” – 18 UNF is a thread having nominal major diameter of 5/8”, 18 threads per inch, and belongs to the fine thread series.
- Screw sizes with diameter under ¼” are numbered (i.e., small screw diameters are designated by gauge sizes, and not by fractions of an inch).
- Unified threads have thread angle of 60.
Fine Threads vs. Coarse Threads
Reading Data Sheets
- Static Load Rating (always stay below) – maximum stationary load before total permanent deformation of the fastener.
- Operating Load Rating (always stay below) - maximum permissible live load before total permanent deformation of the fastener.
Standards (Page link)
- ASTM's fastener standards specify, test, and evaluate the material, dimensional, mechanical, and metallurgical properties of various fasteners. These fastener standards allow manufacturers and users to examine fasteners to ensure their strength and quality for safe utilization1.