Question 1

Threads, Fasteners & Springs — For inch threads, pitch (in inches) equals 1 divided by the threads per inch (TPI); therefore, stating pitch = 12 / TPI is incorrect.

Accepted Answer

Introduction / Context: Pitch is the axial distance from a point on one thread to the corresponding point on the next thread of the same start. In inch systems, threads per inch (TPI) directly determine pitch by a reciprocal relation. Given Data / Assumptions: Unified (inch) thread specification. TPI = number of threads per 1 inch of axial length. Pitch is measured along the axis, same start to next. Concept / Approach: If a screw has TPI threads over one inch, the spacing between adjacent threads is 1/TPI inches. The statement 12/TPI would imply 12 inches per “thread,” which is dimensionally wrong for pitch. Step-by-Step Solution: 1) Define pitch: axial distance between adjacent threads (same start).2) Compute pitch = 1 / TPI.3) Compare with 12 / TPI—this yields twelve times the correct value.4) Conclude the given statement is incorrect. Verification / Alternative check: Example: 20 TPI → pitch = 1/20 = 0.05 in; using 12/20 would give 0.6 in, clearly wrong. Why Other Options Are Wrong: TPI/12 has wrong units; saying pitch is independent of TPI ignores the definition; for multi-start, lead = pitch * starts, but pitch remains 1/TPI for each start. Common Pitfalls: Confusing “lead” with “pitch”; mixing inch and foot units. Final Answer: Incorrect

Question 2

Threads, Fasteners & Springs — Multiple-start threads have two or more ridges; their lead equals pitch multiplied by the number of starts. Saying “one ridge and lead = pitch” is incorrect.

Accepted Answer

Introduction / Context: In multi-start threads, two or more identical helices are interleaved. This design increases the lead for quicker axial travel per revolution, commonly used in quick-open caps or motion mechanisms. Given Data / Assumptions: Number of starts >= 2 for multiple threads. Pitch is measured between adjacent threads on the same start. Lead = pitch * number_of_starts. Concept / Approach: Because multiple ridges exist, the axial advance after one full turn spans across multiple thread spaces of the same start count, hence lead grows proportionally to starts. Step-by-Step Solution: 1) Determine starts by tracing one ridge around the cylinder.2) Measure pitch along that same start.3) Compute lead = pitch * starts.4) Conclude the statement is incorrect since it claims one ridge and lead = pitch. Verification / Alternative check: For a double-start with pitch 2 mm, lead = 4 mm; observation after one turn confirms 4 mm axial movement. Why Other Options Are Wrong: Suggesting one ridge or lead = pitch for all types ignores definitions; dividing pitch by starts reverses the correct relation. Common Pitfalls: Counting pitch across different starts; mistaking lead for thread height. Final Answer: Incorrect

Question 3

Threads, Fasteners & Springs — Rivets are generally classified as permanent fasteners because they are installed by plastic deformation and are not intended to be removed without destruction.

Accepted Answer

Introduction / Context: Fasteners are often categorized as permanent or non-permanent. Riveting forms a mechanical joint by upsetting (deforming) the rivet shank, creating a clamped assembly that is not intended to be disassembled without drilling or destroying the rivet. Given Data / Assumptions: Rivets are set using force/heat to plastically deform the tail. Service requires joint integrity over the life of the assembly. Removal damages the rivet, unlike reusable threaded fasteners. Concept / Approach: Permanence stems from plastic deformation and lack of a reversible mechanism. This differs from screws/bolts, which can be unthreaded, and from welds, which are metallurgical bonds rather than mechanical fasteners. Step-by-Step Solution: 1) Identify the joining method—upsetting a rivet vs threading.2) Assess removability without damage.3) Classify as permanent if removal requires destruction.4) Conclude the statement “not considered permanent” is incorrect. Verification / Alternative check: Maintenance manuals specify drilling out rivets for removal, confirming non-reusability and permanence. Why Other Options Are Wrong: Equating rivets with temporary threaded fasteners is false; welding is unrelated to rivet permanence; color does not determine classification. Common Pitfalls: Assuming blind rivets are reusable; misclassifying lock-bolts (hybrid systems) as threaded when they are also essentially permanent. Final Answer: Incorrect

Question 4

Threads and fasteners — Clarify the definition: Is an “internal thread” the thread formed on the inside (female) surface of a part such as a nut or a tapped hole, or is it located on the outside of a member?

Accepted Answer

Introduction / Context: In mechanical design and technical drawing, threads are categorized as internal (female) or external (male). Confusing these terms can lead to incorrect specifications, mismatched components, and costly rework. This question checks your recall of the formal definition of an internal thread and reinforces the vocabulary used on engineering drawings and in shop practice. Given Data / Assumptions: The statement claims an internal thread is on the outside of a member. We assume standard machine design terminology used across common thread systems (metric ISO, unified UNC/UNF, pipe threads, etc.). Objective: decide whether internal threads are inside or outside a part. Concept / Approach: An internal thread is formed on the inside surface of a hole and is intended to receive a matching external (male) thread, such as a bolt or screw. Typical examples include tapped holes in plates and the threads machined inside a hex nut. By contrast, an external thread is produced on the outside surface of a cylindrical feature (e.g., the shank of a bolt). Drawings label these with standardized callouts that specify thread series, pitch, class of fit, and other particulars. Step-by-Step Solution: 1) Identify the term: “internal thread.”2) Recall the definition: internal = female = inside a part (nut, tapped hole).3) Compare with the statement: it incorrectly places an internal thread on the outside.4) Therefore, the statement is false. Verification / Alternative check: Consider a standard nut-and-bolt pair. The nut clearly contains the thread on its inside surface; this is the internal thread. The bolt carries the external thread on its outside surface. Thread gauges and inspection practices also distinguish “internal” gauges for holes versus “external” gauges for shafts. Why Other Options Are Wrong: Correct: Incorrect because the statement is false. Context-dependent across standards: Naming conventions are consistent across major standards. Only true for tapered threads: Even tapered systems maintain the same inside/outside distinction. True for metric but not for unified threads: Both systems use the same terminology. Common Pitfalls: Mixing up “internal/external” with “right-hand/left-hand”; assuming surface location changes with thread class; overlooking that inserts (e.g., helicoils) still create internal threads in a hole. Final Answer: Incorrect

Question 5

Thread geometry — Is the “major diameter” defined as the largest diameter of a screw thread (e.g., crest-to-crest on an external thread or root-to-root cylinder for an internal thread)?

Accepted Answer

Introduction / Context: Understanding thread diameters—major, pitch, and minor—is essential for specifying fits, calculating strength, and selecting taps/dies. Mislabeling these diameters leads to tolerance stack-up problems and assembly failures. This item focuses on the definition of the major diameter. Given Data / Assumptions: Claim: the major diameter is the largest diameter of a screw thread. Thread systems considered: metric ISO and unified (UNC/UNF), among others. We distinguish external vs internal threads but keep the definition consistent. Concept / Approach: The major diameter is the largest diameter of a thread form. For an external (male) thread such as on a bolt, the major diameter is measured at the crests. For an internal (female) thread such as in a nut or tapped hole, the major diameter corresponds to the imaginary cylinder that touches the roots of the internal thread profile. The pitch (effective) diameter lies between major and minor and is where the thread thickness equals the space between threads. The minor diameter is the smallest diameter of the thread form. Step-by-Step Solution: 1) Recall thread diameter hierarchy: major > pitch > minor.2) Identify what “largest” maps to: major diameter.3) Confirm across thread types: definition remains largest for both internal and external threads.4) Conclude the statement is true. Verification / Alternative check: Check a thread data chart: for M10 × 1.5, the listed major diameter is approximately 10 mm for the external thread; pitch diameter and minor diameter are smaller values. Similar relationships appear in UNC/UNF tables (e.g., 3/8-16 UNC). Why Other Options Are Wrong: Incorrect: Conflicts with formal definitions. Only applies to internal / external: The concept applies to both; only how it is realized (crest vs root cylinder) differs. Refers to pitch diameter: Pitch diameter is not the largest; it is the effective diameter for fit calculations. Common Pitfalls: Confusing pitch diameter with major diameter; assuming crest truncation changes which diameter is “major”; ignoring tolerance classes that slightly shift numeric limits but not definitions. Final Answer: Correct

Threads, Fasteners and Springs Questions