A better way todiscuss threads

By Gary Shelton
Principal Engineer
Exlar Corp.
Chanhassen, Minn.

EDITED BY VICTORIA REITZ

New and innovative machinery components often call for custom thread designs. The problem with custom threads, unfortunately, is that no standards describe their features and details. It is essential that designers, manufacturers, and inspectors all interpret dimensions on drawings in exactly the same way. Questions and confusion invariably arise, whether the subject is surface finish, geometry, or tolerances. How does one look at the part, interpret a dimension for a process, or measure the thread to show the right dimensions? The answer is not as easy as it seems.

For common Unified National or Acme threads there are accepted standards published in handbooks and similar documents. But when designing or manufacturing custom thread forms, if standards have been written, they are few and hard to find. There is a need for the thread design and manufacturing world to publish standards that everyone can agree upon.

In the interim, one solution is a simple diagram that defines certain inspection angles and a few thread details. It is useful to companies and clients because it gives both parties common terminology and eliminates the confusion that those unfamiliar with threads often encounter.