Home 
FAQ Product Terminology Thread Terminology
FAQ Product Terminology Thread Terminology
| Thread Terminology |
 |
 |
|
DIMENSION A
Full diameter shank: Equal to major diameter of thread; produced by a cut thread or by a rolled thread on an extruded blank, usually seen on a machine bolt and cap screw.
DIMENSION B
Undersized shank: Equal to approximately the pitch diameter of thread; produced by roll threading a non-extruded blank.
DIMENSION C
Pitch: The distance from a point on the screw thread to a corresponding point on the next thread, measured parallel to the axis.
DIMENSION D
Major Diameter: The largest diameter of a screw thread.
DIMENSION E
Pitch Diameter: Diameter of screw thread, approximately half-way between the major and minor diameters.
DIMENSION F
Minor Diameter: The smallest diameter of a screw thread.
Thread Fits Are:
CLASSES 1A and 1B: For work of rough commercial quality where loose fit for spin-on-assembly is desirable.
CLASSES 2A and 2B: Recognized standard for normal production of the great bulk of commercial bolts, nuts and screws.
CLASSES 3A and 3B: Used where a closed fit between mating parts for high quality work is required.
CLASS 4: A theoretical rather than practical class, now obsolete.
CLASS 5: For a wrench fit. Used principally for studs and their mating tapped holes. A force fit requiring the application of high torque for semi-permanent assembly.
Other Terminology:
LEAD: The distance a screw thread advances axially in one turn.
CUT THREAD: Threads are cut or chased; the unthreaded portion of shank will be equal to major diameter of thread.
ROLLED THREAD: Threads are cold formed by squeezing the blank between reciprocating serrated dies. This acts to increase the major diameter of the thread over and above the diameter of unthreaded shank (if any), unless an extruded blank is used.
The following chart represents industry standard designations for thread types.
|
