Threads and fasteners: A thread that is formed on the inside surface of a cylindrical or tapered hole (for example, a tapped hole) is called what type of thread?

Introduction / Context:
Screw threads may occur on bolts (external) or in tapped holes and nuts (internal). Correct terminology ensures accurate callouts, tooling, and inspection.

Given Data / Assumptions:

• The thread is located inside a part (for example, a nut or a tapped hole).
• We distinguish between internal versus external thread forms.
• Standard terms are used (major/minor diameters describe sizes, not locations).

Concept / Approach:

An internal thread is machined or formed on the interior surface and mates with an external thread. Drawings specify series (e.g., UNC/UNF), size, class (e.g., 2B for internal), and depth or through condition.

Step-by-Step Solution:

Verification / Alternative check:

Standards (such as ASME/ISO) use “A” classes for external and “B” for internal in Unified threads, reinforcing the location-based terminology.

Why Other Options Are Wrong:

Basic thread: generic phrase, not a location.

External thread: opposite of inside location.

Major diameter thread: refers to the largest diameter of a thread, not the thread’s location.

Common Pitfalls:

Confusing diameter terms (major/minor/pitch) with internal/external classification.

Final Answer:

Internal thread