AIT Blueprint Reading 5 — Questions and Answers
Question 1: When a blueprint dimension shows '3/4" – 10 UNC – 2B', what does this callout describe?
- A pipe fitting with 10 grooves
- A 3/4-inch diameter screw thread, 10 threads per inch, Unified National Coarse, class 2 fit (internal) (Correct answer)
- A bolt pattern 3/4 inches from center with 10 bolts
- A welded rod 3/4 inch wide, 10 inches long
Correct answer: A 3/4-inch diameter screw thread, 10 threads per inch, Unified National Coarse, class 2 fit (internal)
This thread callout specifies a 3/4-inch diameter, 10 TPI (threads per inch), Unified National Coarse series, Class 2 fit for an internal (female) thread.
Question 2: What does a zigzag or wavy break line on a blueprint indicate?
- A surface that requires grinding
- A long object that has been shortened to fit on the drawing (Correct answer)
- A crack or flaw in the material
- A seismic expansion joint
Correct answer: A long object that has been shortened to fit on the drawing
A break line (wavy or zigzag) indicates that a long object has been shortened on the drawing while maintaining the correct overall dimensions in the notes.
Question 3: In a floor plan blueprint, what does the symbol of a thin rectangle with diagonal lines inside typically represent?
- A window opening
- A door swing path
- Insulation within a wall cavity (Correct answer)
- A glass block or skylight
Correct answer: Insulation within a wall cavity
In construction drawings, a rectangle with diagonal hatching inside a wall cavity represents batt insulation.
Question 4: What is a 'datum' in the context of blueprint dimensions and GD&T?
- The total tolerance allowed on a part
- A theoretically exact reference point, axis, or plane from which measurements are taken (Correct answer)
- The scale factor used on the drawing
- The date the drawing was last revised
Correct answer: A theoretically exact reference point, axis, or plane from which measurements are taken
A datum is an exact reference feature (point, line, or plane) used as the starting point for measurements and geometric tolerances on a part.
Question 5: On a blueprint callout reading '4X Ø0.500 ↧ 0.750', what does the '4X' signify?
- Four times the diameter should be drilled
- There are four identical holes to be machined (Correct answer)
- The feature is four times larger than shown
- The drill makes four passes
Correct answer: There are four identical holes to be machined
'4X' before a feature callout means the operation or feature is repeated four times (four identical holes of 0.500" diameter drilled to 0.750" depth).
Question 6: What does the term 'as-built drawings' refer to in construction?
- The original architect's concept sketches
- Drawings updated to reflect actual field conditions and changes made during construction (Correct answer)
- Blueprints approved by the building inspector
- Computer-generated 3D models of the finished structure
Correct answer: Drawings updated to reflect actual field conditions and changes made during construction
As-built drawings are revised blueprints that record the actual constructed conditions, including any field changes made during the project.
Question 7: On a structural blueprint, what does the notation 'EQ. SP.' between dimension lines mean?
- Equipment Specification
- Equal Spacing — the elements between those points are evenly distributed (Correct answer)
- Expansion Splice Point
- Exterior Square Panel
Correct answer: Equal Spacing — the elements between those points are evenly distributed
'EQ. SP.' means Equal Spacing, indicating that the elements (such as columns, studs, or bolts) between the indicated points are evenly distributed.
AIT Blueprint Reading 5
When a blueprint dimension shows '3/4" – 10 UNC – 2B', what does this callout describe?