Stove bolts and machine screws are sized by diameter, threads per inch, and length.

• A. True
• B. False
• C. Diameter only
• D. Diameter, threads per inch, and length

Answer: (D)

Stove bolts and machine screws use three measurements because each one controls a different aspect of how the fastener fits and works in a joint. The diameter is the size of the thread itself, which determines what nut or tapped hole will fit. The threads per inch describe the pitch—the distance between threads—so you know how coarse or fine the thread is and how it will engage. The length indicates how long the fastener is from under the head to the tip, showing how much of the screw will extend through the parts and how much thread will engage.

For example, a fastener described as 1/4-20 x 1 inch has a 1/4 inch major diameter, 20 threads per inch, and a total length of 1 inch. This three-part sizing is standard for inch-based fasteners; metric sizing uses diameter and pitch in millimeters plus length.