Fasteners: 64 flashcards
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1. What is a screw?
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A screw is a simple machine that converts rotational motion into linear motion, typically used to fasten objects or transmit force.
2. What is the purpose of a screw thread?
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A screw thread provides a helical ridge that allows the screw to advance into a material when rotated, creating a strong fastening force.
3. Define pitch of a screw thread.
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The pitch is the axial distance between adjacent threads, measured parallel to the screw axis.
4. What is the lead of a screw?
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The lead is the axial distance the screw advances in one complete revolution.
5. How are pitch and lead related for a single-start thread?
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For a single-start thread, lead = pitch.
6. How are pitch and lead related for a double-start thread?
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For a double-start thread, lead = 2 × pitch.
7. What is the major diameter of a screw thread?
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The major diameter is the largest diameter of the screw thread, measured across the crests.
8. What is the minor diameter of a screw thread?
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The minor diameter is the smallest diameter of the screw thread, measured across the roots.
9. What is the pitch diameter of a screw thread?
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The pitch diameter is the diameter at which the thread thickness equals the thread spacing, approximately midway between major and minor diameters.
10. What is a thread crest?
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The crest is the top surface of the thread, where the thread is highest.
11. What is a thread root?
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The root is the bottom surface of the thread, where the thread is lowest.
12. What is thread depth?
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Thread depth is the radial distance between the crest and the root of a thread.
13. What is the thread angle?
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The thread angle is the angle between the flanks of the thread, measured in an axial plane.
14. What is a right-hand thread?
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A right-hand thread advances into the material when turned clockwise and is the standard for most screws.
15. What is a left-hand thread?
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A left-hand thread advances when turned counterclockwise, used in special applications to prevent loosening.
16. What is a single-start thread?
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A single-start thread has one continuous helical thread, providing high friction and self-locking, but slow advancement.
17. What is a multi-start thread?
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A multi-start thread has two or more independent helical threads, allowing faster axial movement per revolution.
18. What is the mechanical advantage of a screw?
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The mechanical advantage (MA) of a screw is the ratio of the force applied at the handle to the force exerted by the screw, approximately $MA = \frac{2\pi r}{p}$, where $r$ is the handle radius and $p$ is the pitch.
19. What is the efficiency of a screw?
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Efficiency is the ratio of output work to input work, often reduced by friction; it can be calculated as $\eta = \frac{MA_{\text{ideal}}}{MA_{\text{actual}}}$.
20. What is a screw thread standard?
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A screw thread standard defines the geometry, dimensions, and tolerances of threads to ensure interchangeability, such as ISO metric or Unified threads.
21. What does ISO metric thread designation M10 × 1.5 mean?
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It means a metric thread with major diameter 10 mm and pitch 1.5 mm.
22. What is the difference between a bolt and a screw?
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A bolt is typically used with a nut to fasten two unthreaded parts, while a screw threads into one of the parts being fastened.
23. What is a machine screw?
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A machine screw is a small screw with a uniform diameter and threaded along its entire length, used in tapped holes.
24. What is a cap screw?
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A cap screw is a large screw with a cylindrical head and hexagonal socket, used for high-strength fastening.
25. What is a set screw?
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A set screw is a headless screw used to secure an object within or against another object, often by friction.
26. What is a lag screw?
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A lag screw is a large, heavy-duty wood screw with a hexagonal head, used for fastening wood to wood or wood to masonry.
27. What is a self-tapping screw?
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A self-tapping screw can cut its own thread as it is driven into a material, eliminating the need for pre-tapping.
28. What is a thread tap?
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A tap is a tool used to cut internal threads in a hole.
29. What is a die?
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A die is a tool used to cut external threads on a cylindrical rod.
30. What is the purpose of a thread pitch gauge?
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A thread pitch gauge is used to measure the pitch of a thread by comparing it with standard profiles.
31. What is thread engagement?
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Thread engagement is the length of contact between mating threads, which affects the strength of the fastened joint.
32. What is a thread relief?
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A thread relief is a groove at the end of a thread to provide a clean runout and prevent stress concentration.
33. What is a thread chamfer?
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A chamfer is a tapered edge at the start of a thread to facilitate engagement and prevent cross-threading.
34. What is cross-threading?
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Cross-threading occurs when threads are misaligned during assembly, causing damage to the threads and weakening the joint.
35. What is thread galling?
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Galling is a form of wear caused by adhesion between sliding surfaces, often occurring in stainless steel threads under high pressure.
36. What is a thread insert?
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A thread insert is a repair or reinforcement device installed into a stripped hole to provide new threads.
37. What is the purpose of a lock washer?
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A lock washer prevents a screw or nut from loosening due to vibration by providing tension or biting into the surface.
38. What is a nut?
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A nut is a fastening element with an internal thread, used with a bolt to clamp parts together.
39. What is a washer?
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A washer is a thin disk placed under a nut or screw head to distribute load, reduce friction, or seal.
40. What is the difference between a coarse and fine thread?
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Coarse threads have larger pitch (fewer threads per inch) and are stronger against stripping; fine threads have smaller pitch and are better for vibration and thin-walled parts.
41. What is the thread series designation UNC?
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UNC stands for Unified National Coarse, a standard for coarse threads in the Unified Thread Standard.
42. What is the thread series designation UNF?
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UNF stands for Unified National Fine, a standard for fine threads in the Unified Thread Standard.
43. What is a screw's root diameter?
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The root diameter is the diameter of the cylinder that forms the bottom of the thread, also known as minor diameter.
44. What is the flank of a thread?
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The flank is the surface of the thread that connects the crest and the root.
45. What is thread pitch diameter?
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The pitch diameter is the diameter of an imaginary cylinder where the width of the thread and the width of the space between threads are equal.
46. What is the formula for thread depth in terms of pitch for a sharp V-thread?
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For a sharp V-thread, depth $h = 0.866 \times p$, where $p$ is the pitch.
47. What is the formula for pitch diameter for a metric thread?
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Pitch diameter $d_2 = d - 0.6495 \times p$, where $d$ is major diameter and $p$ is pitch.
48. What is the purpose of a thread's helix angle?
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The helix angle is the angle of the thread relative to the axis; it affects the mechanical advantage and self-locking behavior.
49. What is a screw's self-locking condition?
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A screw is self-locking if the friction angle is greater than the helix angle, preventing it from unscrewing under load.
50. What is the difference between a screw and a helical gear?
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A screw converts rotation to linear motion, while a helical gear transmits power between parallel or crossed shafts with smooth engagement.
51. What is a ball screw?
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A ball screw uses recirculating ball bearings between the screw and nut to reduce friction and provide high efficiency and precision.
52. What is a lead screw?
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A lead screw is a threaded rod that converts rotational motion to linear motion, often used in lathes and vises.
53. What is an Acme thread?
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An Acme thread is a trapezoidal thread with a 29° angle, used for power transmission due to its strength and ease of manufacture.
54. What is a buttress thread?
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A buttress thread is asymmetric, designed to handle high thrust in one direction, often used in vises and jacks.
55. What is a square thread?
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A square thread has a square profile, providing high efficiency and minimal radial pressure, but is difficult to manufacture.
56. What is the purpose of thread lubrication?
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Lubrication reduces friction and wear during assembly, preventing galling and ensuring proper torque-tension relationship.
57. What is torque in the context of screws?
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Torque is the rotational force applied to a screw to generate clamping force (preload) in the joint.
58. What is preload in a bolted joint?
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Preload is the tension created in a bolt when tightened, which clamps the parts together and resists external loads.
59. What is the relationship between torque and preload?
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Torque $T$ is related to preload $F$ by $T = K \cdot F \cdot d$, where $K$ is the nut factor and $d$ is nominal diameter.
60. What is a thread's minor diameter used for?
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The minor diameter is used to calculate the tensile stress area and determine the strength of the threaded portion.
61. What is the tensile stress area of a screw?
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The tensile stress area is the effective cross-sectional area used to calculate the load-carrying capacity of a threaded fastener, approximately $A_t = \frac{\pi}{4} \left( d - 0.9382 \times p \right)^2$ for metric threads.
62. What is a thread class?
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A thread class defines the tolerance and fit between mating threads, such as 1A, 2A, 3A for external threads and 1B, 2B, 3B for internal threads.
63. What is the difference between a screw and a bolt?
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A screw is typically turned into the material being fastened, while a bolt passes through a hole and is secured with a nut.
64. What is a thread's root radius?
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The root radius is the curvature at the bottom of the thread, which reduces stress concentration and improves fatigue life.
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