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ACME Thread Calculator (General Purpose)
General-purpose ACME threads are covered by
ASME B1.5. For reduced-height threads (thin-wall parts), see
Stub ACME (ASME B1.8).
Use this ACME thread calculator to get external (rod) and internal (nut) limiting dimensions for general‑purpose ACME screw threads per ASME B1.5.
Choose a thread size, tolerance class (2G/3G/4G) and number of starts (single/multi‑start) to see major, pitch and minor diameter limits instantly.
Tip: If you are comparing general ACME vs stub ACME, use the calculators on this page and the linked pages below to avoid mixing standards.
Inputs
Multi‑start uses the same basic pitch (P) but increases lead (L = starts × P).
mm = inch × 25.4
Example buttons load a common size if it exists in the table.
What is calculated
- External (rod): major diameter (max/min), pitch diameter (max/min), minor diameter (max/min).
- Internal (nut): major diameter (max/min), pitch diameter (max/min), minor diameter (max/min).
- Basic values: pitch P = 1/TPI, basic pitch diameter D2 = D − 0.5P, basic minor diameter D1 = D − P.
Thread angle is 29°. h = P/2 (general‑purpose ACME).
ACME vs Stub ACME and tolerance classes
General‑purpose ACME (ASME B1.5) commonly uses class 2G. Choose 3G or 4G when you need a tighter fit and less backlash.
Stub ACME (ASME B1.8) uses a shallower thread form and is used when you need a coarse pitch with reduced thread depth.
How to use this calculator
- Select a thread size (diameter–TPI).
- Select tolerance class.
- For general ACME, choose the number of starts if you have a multi‑start lead screw.
- Read the rod/nut limits, then compare min/max clearance at the pitch diameter if needed.
Related tools
Reference
ASME B1.5 (ACME Screw Threads) and Machinery’s Handbook.
What is an ACME thread?
An ACME thread is a 29° trapezoidal screw thread used primarily for power transmission (lead screws, jacks, vises and linear actuators).
Compared with 60° V-threads, the trapezoidal profile provides stronger thread flanks and improved wear characteristics for sliding contact applications.
ACME vs Stub ACME (quick comparison)
| Feature | General ACME | Stub ACME |
|---|
| Standard | ASME B1.5 | ASME B1.8 |
| Included angle | 29° | 29° |
| Thread height (typical) | Higher (general form) | Reduced height (stub form) |
| When to use | General power screws | Thin-wall parts / limited depth |
ACME thread profile and formulas
This page shows limiting dimensions from embedded tables. For engineering checks, it also helps to know the basic geometry terms:
P (pitch), n (TPI), Lead (starts × pitch) and the basic diameters.
Multi-start threads have the same pitch as the selected TPI but a larger lead.
- P = 1 / TPI
- Lead = Starts × P
- Major diameter, pitch diameter and minor diameter limits are taken from ASME B1.5 tables for the selected size and class.
Tolerance classes (2G, 3G, 4G)
General-purpose ACME threads use tolerance classes such as 2G, 3G and 4G.
For the same nominal size and pitch, tighter classes typically reduce backlash but require better control of manufacturing variation and plating allowance.
FAQ
Which standard defines general-purpose ACME threads?
General-purpose ACME thread dimensions and tolerances are defined in ASME B1.5.
What is the difference between ACME and Stub ACME?
Stub ACME uses a reduced thread height and is defined in ASME B1.8. It is often chosen for thin-wall parts or limited thread depth.
What does multi-start mean?
Multi-start threads have two or more helical starts. The pitch (from TPI) stays the same, but the lead increases by the number of starts.