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Metric Thread Dimensions Calculator
Metric thread calculator to calculate external and internal metric thread dimensions including major diameter, minor diameter,
pitch diameter and thread tolerance according to ISO 724 and ISO 965 standards.
There are two calculation options available, general engineering use or custom use.
In general engineering use, calculations can be done by selecting a standard metric thread size in a range from 1.6 mm (M1.6) to 64 mm (M64).
Tolerance class can be selected among the alternatives 6e, 6f, 6g and 4h for bolts and 5H, 6H, 7H and 6G for nuts. 6g and 6H are default values and selected class for commercial external threads and internal threads in ISO 965-1:1998.
The user shall use 6g for bolts and 6H for nuts unless there is a specific requirement to use other tolerance classes.
In custom use, thread size, pitch and tolerance classes can be independently selected for custom metric thread dimensions calculations.
Some important notes from ISO metric thread standards:
- External Screw Thread Designation: Nominal Diameter x Pitch - Tolerance class for pitch diameter
- Tolerance class for major diameter (M10 x 1 5g 6g)
- Internal Screw Thread Designation: – Nominal Diameter x Pitch - Tolerance class for pitch diameter
- Tolerance class for minor diameter (M10 x 1 5H 6H)
- If the two class designations for the pitch diameter and crest diameter are the same it is not necessary to repeat the symbols. (M10 x 1 6g)
- According to ISO 1
, standard reference temperature for geometrical product
specification is 20 °C.
- Gauges and gauging for ISO general purpose metric threads are defined in the ISO 1502
standard.
- The list of metric
screw thread used in general engineering applications are given in the
General
Purpose Metric Screw Threads Table.
Basic pitch diameter d2 (mm)
—
Basic minor diameter d1 (mm)
—
Symbols & terms (d, D, d2, D2, d3, D1)
| Symbol | Term | Thread |
|---|
| d | Major diameter (basic) | External (bolt) |
| d2 | Pitch diameter (basic) | External (bolt) |
| d3 | Minor diameter at root (external) | External (bolt) |
| D | Major diameter (internal) | Internal (nut) |
| D2 | Pitch diameter (internal) | Internal (nut) |
| D1 | Minor diameter (internal) | Internal (nut) |
| P | Pitch | Both |
| H | Fundamental triangle height | Both |
| C | Crest truncation (clearance) | External (bolt) |
| Rmin | Minimum root radius (high strength fasteners) | External (bolt) |
Tip: Many searches use “D1/D2” for internal threads and “d2/d3” for external threads. This table makes the mapping explicit.
External thread limits
Internal thread limits
ISO Metric Thread Profile and Formulas
ISO metric screw threads use the basic profile defined in ISO 68-1.
The external thread root contour is defined in ISO 965-1 (positions e, f, g).
Use the formulas below to understand how d, d2, d1 (external) and
D, D2, D1 (internal) relate to pitch P.
ISO metric screw thread basic profile (ISO 68-1)
ISO external thread root contour (ISO 965-1) for positions e, f, g
Metric thread formulas (quick reference)
| Parameter |
Equation |
| Fundamental triangle height (H) |
H = (√3 / 2) · P |
| Basic pitch diameter (d2, D2) |
d2 = D2 = d − 2·(3/8)·H = D − 2·(3/8)·H |
| Basic minor diameter (d1, D1) |
d1 = D1 = d − 2·(5/8)·H = D − 2·(5/8)·H |
| External min truncation (Cmin) |
Cmin = 0.125 · P |
| External max major diameter (dmax) |
dmax = d + es |
| External min major diameter (dmin) |
dmin = dmax − Td |
| External max pitch diameter (d2max) |
d2max = d2 + es |
| External min pitch diameter (d2min) |
d2min = d2max − Td2 |
| Internal min major diameter (Dmin) |
Dmin = D + EI |
| Internal min pitch diameter (D2min) |
D2min = D2 + EI |
| Internal max pitch diameter (D2max) |
D2max = D2min + TD2 |
| Internal min minor diameter (D1min) |
D1min = D1 + EI |
| Internal max minor diameter (D1max) |
D1max = D1min + TD1 |
Note: es and EI are fundamental deviations.
Td, Td2, TD1, TD2 are ISO tolerance values
for major, pitch, and minor diameters (external/internal).
FAQ
What are the thread dimensions for M10 x 1.5 (6H / 6g)?
Select M10x1.5 (or enable custom and enter 10 / 1.5) and choose classes like 6H and 6g.
Where can I find M3 minor diameter?
Select M3x0.5 and read the internal D1 limits or external d3 limits.
Note-1: For coated threads, the tolerances apply to the parts before coating,
unless otherwise stated. After coating, the actual thread profile shall not at
any point transgress the maximum material limits for positions h or H. For external (bolt) threads; The actual root contours shall not at any point transgress the basic
profile. Fasteners of property class 8.8 and higher (see ISO 898-1), the root profile shall have a non-reversing
curvature, no portion of which shall have a radius of less than Rmin.
Definitions:
Basic profile: The theoretical profile of a screw thread in an axial plane defined by theoretical dimensions and angles
common to internal and external threads
Crest: The surface at the top of the ridge connecting its two flanks.
Gauges and Gauging: Details for the
manufacture and use of gauges for checking ISO general-purpose metric screw threads are specified in the ISO 1502:1996 standard. It specifies the features of the types of gauges (Solid/adjustable GO screw ring gauges, check plugs, setting plugs, wear check
plugs, screw caliper gauges, plug gauges, etc.) which are recommended for checking
external and internal screw threads of workplaces and
for the setting and checking of certain of the screw
gauges.
Major Diameter: The maximum
diameter of a thread which is diameter of the crest of a male thread or root of
a female thread.
Minor Diameter: The minimum
diameter of a thread which is diameter of the root of a male thread or crest of
a female thread.
Root: The surface at the bottom of the groove connecting the adjacent flanks
Thread pitch: The distance
between two adjacent threads.
Supplements:
-
Oberg,
E. , Jones ,F.D. , Horton H.L. , Ryffel H.H., (2016) .
Machinery's Handbook
. 30th edition. Industrial Press Inc.
- ISO 1:2002 - Geometrical Product Specifications (GPS) - Standard reference temperature for geometrical product specification and verification
- ISO 68-1:1998 (E) - ISO general purpose screw threads — Basic profile — Part 1: Metric screw threads
- ISO 262:1998 (E) - ISO general purpose metric screw threads — Selected sizes for screws, bolts and nuts
- ISO 724:1993 (E) - ISO general-purpose metric screw threads - Basic dimensions
- ISO 965-1:1998 – ISO General Purpose Metric Screw Threads – Tolerances Part-1: Principles and Basic Data
- ISO 965-2:1998 – ISO General Purpose Metric Screw Threads – Tolerances Part-2: Limits of sizes for general purpose external and internal screw threads - Medium quality
- BS 3643-1:2007 – ISO General Purpose Metric Screw Threads – Tolerances Part-1: Principles and Basic Data (British Standard)