Topics Introduction Terminology Thread Specifications Bolts and Screws MECH 1200 Introduction Terminology Thread Specifications Bolts and Screws Nuts and Locking Devices Exercise Questions Note: Refer to Chapter 6 in the text.

Introduction There are two thread standards: MECH 1200 There are two thread standards: The Unified Screw Thread Standard: Used in the U.S. It is based on a 60o thread angle. Unified National Coarse (UNC) series: this is the most common series. Bolts, screws, and nuts of this series are used for general applications in which a quick assembly is required. Unified National Fine (UNF) series: threads of this series are used for handling high tensile stresses, or when the length of engagement is limited such as screws in thin walls. Unified National Special (UNS) series The International Screw Thread Standard: most common standard, based also on the 60o thread angle.

Terminology MECH 1200 Thread angle: the angle included between the sides of the thread, The ISO thread angle is 60 degrees. Pitch: the distance between one point on a thread to the corresponding point on the next thread. Number of threads per inch Minor (root) diameter Major (Outside) diameter Lead: the distance a screw thread advances in one revolution. Thread Fit: How tight is the thread engagement. Three classes of fit are used in the unified system, loose, medium, and tight fits. A for external and B for internal fits. (see p. 110) Source: Siemens Technik Akademie Berlin

Thread Specifications MECH 1200 Unified system threads: Example: ¼ - 20 UNC-BX1 indicates a thread with an outer diameter is ¼ inch, with 20 threads per inch, the type of thread is UNC, and a B (internal) fit and a thread length of 1 inch. Metric system threads: Example: M10 ×1.5-6g indicates a Metric thread with an outside diameter of 10 mm and a pitch of 1.5 mm, the fit of the thread is 6g. Bolts and Screws: The two words are used interchangeably, but generally, bolt is used when a nut is required to be used. The shank of a bolt has a diameter that is equal to the major diameter. Source: Siemens Technik Akademie Berlin

Common Bolts and Screws MECH 1200 Carriage Bolt used to fasten metal to wood. It has a square body right under the head to keep the wood from turning. Machine Screw used for vehicle body and metal sheets Sheet Metal Screw Set Screw usually has no head, used to lock pulleys or gears to shafts Socket Head Screw has the strongest head style

Has a reduced shank, used for applications in which shock loads occur. MECH 1200 Stud (Standing) Bolt has threads on both ends, screwed permanently in one end and a nut on the other end. Hexagon Through Bolt Hexagon Fit Bolt If the bolt goes through all parts and is fastened with a nut, then it is called a Through Bolt. When used to fix a part in position against movement it is called a Fit Bolt. Anti-Fatigue Bolt Has a reduced shank, used for applications in which shock loads occur. Source of images in this slide: Siemens Technik Akademie Berlin

Nuts MECH 1200 Hex nuts: Have a hexagonal shape, and has different grades Castle Nut: Named so because it looks like a castle, used in applications where heavy vibrations occur, such as on wheels. Can handle light torques.only. Wing nuts Cap (Acorn) Nut

Fastener Locking Devices MECH 1200 Screw locking devices are used to keep the nut from getting loose. They can be friction based or non-friction based: Friction based Locking devices Internal tooth lock washer External tooth lock washer Spring lock washer Lock washer Safety wires Non-Friction based Locking devices Split pins Nut lock plate Tab washer

Exercise Questions What are the two thread standards? MECH 1200 What are the two thread standards? The Unified Screw Thread System and the ISO metric thread standard. Thoroughly describe the bolt given by: ¼ - 28 UNF 2A The bolt has an outer diameter of ¼ inch and a fine thread of 28 threads per inch (Unified National Fine thread series) and has a medium fit with external thread. Thoroughly describe the thread bolt given by: M10 x 1.25 The bolt is metric and its outer diameter is 10 mm and has a pitch of 1.25 mm

If a thread has 40 threads per inch what is its pitch? MECH 1200 If a thread has 40 threads per inch what is its pitch? Pitch = 1 inch / 40 = 0.025 Is each of the screw locking devices below friction based or not? Yes No Yes No No

What is the component shown in the figure below? MECH 1200 What is the component shown in the figure below? Castle Nut: used in applications that require low amount of torque, and where vibrations are common.