Manufacturing Geometry Tool

Internal ACME & Stub ACME Thread Calculator

Calculates lead, helix angle, and the basic 29° internal thread-form depth and flats. Helix angle is based on the lead and the estimated pitch diameter from the entered major and minor diameters.

Thread Inputs

Inch system
TPI
Fractional values such as 3.5 are supported.
start
Lead equals pitch multiplied by starts.
in
Diameter at the internal-thread roots.
in
Diameter at the internal-thread crests.
Input geometry is valid.

Calculated Motion & Helix

Live output
Lead
—
—
Helix angle at estimated pitch Ø
—
—
Entered radial thread depth
—
—

General-Purpose ACME Basic Form

29°
Thread depth — —
Crest width — —
Root width — —

Standard Stub ACME Basic Form

29° shallow
Thread depth — —
Crest width — —
Root width — —

Manufacturing Check

Entered geometry vs. basic forms
Parameter Inches Millimeters
Pitch — —
Estimated pitch diameter — —
Helix angle at major diameter — Lowest across depth
Helix angle at minor diameter — Highest across depth
Depth difference from ACME basic — —
Depth difference from Stub basic — —
Implied symmetric flat from entered depth — —
ACME STUB ACME h = 0.5P h = 0.3P
Relative profile-depth comparison; not a tolerance or gage drawing.
Formulas, assumptions, and manufacturing limitations

These are basic symmetrical 29° thread-form calculations. The crest and root widths shown are basic flats, not final class-of-fit limits. Actual internal-thread root width and diameters can change with pitch-diameter allowance, class, major/minor diameter clearance, truncation, tool nose radius, and the selected standard limits.

Pitch P = 1 / TPI Lead L = P × number of starts Estimated pitch Ø = (major Ø + minor Ø) / 2 Helix angle λ = atan[L / (π × pitch Ø)] ACME depth h = 0.5000P ACME basic crest/root flat = 0.3707P Stub ACME depth h = 0.3000P Stub basic crest/root flat = 0.4224P

For cutter-clearance review, the helix angle is also calculated at both entered diameters. The angle is highest at the minor diameter of an internal thread. Tool side and heel clearance must exceed the local effective helix requirement with suitable margin, and left-hand versus right-hand cutting may require mirrored relief.

Engineering note: use the applicable ASME B1.5 or ASME B1.8 dimensional limits and inspection requirements before releasing production tooling. This calculator intentionally does not assign fit class, allowance, tolerances, or gage limits.

Results copied.