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Keystone Threaded Products | The Acme Threading Specialists

Common Terminology for Thread Rolling


Thread rolling is widely accepted as the fastest and prefered method of economically producing uniform smooth, precise threads of superior physical qualities.

This process is also capable of performing non-threading operations such as burnishing, knurling and rolling of helical and annular grooves of various forms.

Thread rolling utilizes hardened steel rolls to produce external threads. The working surfaces of the rolls have a thread form which is the reverse of the thread to be produced. In penetrating the surface of the blank, the rolls displace material to form the thread roots, and force the displaced material radically outward to form the thread crests.


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Material Savings

The diameter of the blank is between the major and minor diameters of the threads and varies with the material, type of thread and thread specifications


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Cold working of metal during thread rolling improves thread form physical characteristics and mechanical properties. When thread is rolled, the structure is deformed and the surface is hardened. Increased surface hardness result in thread form properties that are superior to those of the original material.

The above diagram shows how grain structure is maintained with rolled threads, in continuous unbroken lines following contours, increasing tensile and shear strength.

Approximate Percentage of Material Saved by Thread Rolling vs. Cut Threading

1/4" - 20 25% 5/8" - 11 18.75%
5/16" - 18 22% 2 1/4" - 4 1/2 14%


The smooth flanks of rolled threads provide better surface contact with mating threads. The burnished roots and flanks are free from chatter, tearing or cutter marks that can serve as a focal point of stress and starting point for fatigue failures.


Rolled threads maintain consistently closer tolerances and uniformity than cut thread. Thread rolling is unique in its ability to maintain accuracy of the original set up during long runs of high-speed production. Dies do not change appreciably during the life of the rolls. They do not wear like other types of threading tools.


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Definitions of Thread Terms

Class of Thread: An alphanumerical designation to indicate the standard grade of tolerance and allowance specified for a thread.

Crest: The top surface joining the two sides of the thread.

Depth of Thread Engagement: The radial distance, crest to crest, by which the thread forms overlap between two assembled mating threads.

Helix Angle: The angle made by the helix, or conical spiral. Of the thread at the pitch diameter with a plane perpendicular to the axis.

Major Diameter: The major diameter is that of the major cylinder-distance across the crests of the thread.

Minor Diameter: The minor diameter is that of the minor cylinder-root diameter of the thread.

Nominal Size: The designation that is used for general identification of a thread based on the major diameter.

Pitch: The axial distance from a point on one screw thread to the corresponding point on the next screw thread. Pitch is equal to the lead divided by the number of thread starts.

Pitch Diameter: On a straight screw thread, the diameter of an imaginary cylinder the surface of which would pass through the threads at such points as to make equal the width of the threads and the width of the spaces cut by the surface of the cylinder. On a taper screw thread, the diameter, at a given distance from a reference plane perpendicular to the axis of an imaginary cone, the surface of which would pass through the threads at such points as to make equal the width of the threads and the width of the spaces cut by the surface of the cone.

Profile of Thread: The contour of a screw thread ridge and groove delineated by a cutting plane passing through the thread axis, also called form of thread.

Root: The bottom surface joining the two sides of the thread.

Root Diameter: The diameter of an imaginary cylinder bounding the bottom of the roots of a screw thread (minor diameter of the thread).

Thread Series: Groups of diameter/pitch combinations distinguished from each other by the number of threads per unit of measurement.

For custom threading to your specifications, please contact our knowledgeable sales staff.

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