THREAD REFERENCE HUB

Use this hub to identify the thread information you need before choosing a tap, threading insert or feed rate. A thread designation describes more than nominal diameter: pitch, thread family, tolerance class and inspection requirements also matter.

Start with the drawing’s thread callout

Record the full designation, whether the thread is internal or external, the required length and any gauging notes. A nominal pipe size is not a measured outside diameter. Do not substitute one thread family for another because the diameters appear close.

Pitch, lead and threading feed

Pitch is the spacing between adjacent thread forms. Lead is the axial travel in one revolution. For a single-start thread, lead equals pitch; for multiple starts, lead equals pitch multiplied by the number of starts.

For inch threads, pitch in inches = 1 / threads per inch. For metric threads, pitch is usually stated in millimetres. Synchronous feed per minute = spindle RPM × lead, using compatible units. Use the thread lead and feed calculator or tapping calculator to check the arithmetic.

Choose the right reference

• Unified inch and metric screw threads: use the drawing’s specified thread standard and tolerance class. Start with our cutting and forming tap guide when preparing the hole.
• ACME and other power-screw forms: confirm the exact profile, starts, clearances and inspection method with the design specification.
• Pipe threads: check the specific thread family, taper and gauging requirements in our pipe thread reference.
• Wire inserts: the receiving thread uses an STI tap and is different from the finished screw thread. Read the wire-insert preparation guide.

Before machining

Confirm the actual tool’s cutting data, the control’s feed mode and the thread’s inspection requirements. Calculator results provide arithmetic, not class-specific thread limits. Obtain specification-controlled dimensions and gauges from the applicable standard or approved drawing.

Source references

Sandvik Coromant: thread-turning application tips · ASME: general-purpose inch pipe threads.