METRIC THREAD SIZE AND TOLERANCE CALCULATOR (ISO M THREAD)


Metric thread size and tolerance calculator was developed to calculate major, minor and pitch diameters of the external (bolt) and internal (nut) metric threads according to ISO 724:1993 standard. In addition to basic size calculations of metric threads, tolerance calculations of different tolerance classes can be done according to ISO 965-1:1998 and ISO 965-2:1998 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 from the list which contains metric thread sizes in the diameter 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 engineering calculations.

Some important notes from ISO metric screw threads 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 1:2002 , standard reference temperature for geometrical product specification is 20  °C.

- Gauges and gauging for ISO general purpose metric threads are defined in the ISO 1502:1996 standard.

- The basic profile of ISO general purpose metric screw threads is defined in the ISO 68-1:1998 and given in the first figure below.  External (bolt) thread root profile is given the "Definitions" section.  The list of metric screw thread used in general engineering applications are given in the General Purpose Metric Screw Threads Table.

Note: For more information on Metric screw threads including thread form, definitions, limits and fits for threads, standard series and combinations, thread designation, basic dimensions, dimensional effect of coating, formulas and details of MJ profile, please refer to pages 1878 - 1902 of Machinery's Handbook, 29th.

The basic profile for ISO general purpose metric screw threads
ISO metric screw thread basic profile according to ISO 68-1

Calculator:

INPUT PARAMETERS
Calculation Type
GENERAL ENGINEERING USE
Metric Thread
External Thread (Bolt)
Tolerance Class *
Internal Thread (Nut)
Tolerance Class**
CUSTOM USE
Bolt
(External Thread)		 Nominal
Dia.		 Pitch Bolt Tolerance Class
M Pitch Diameter
Tolerance		 Major Diameter
Tolerance
Grades Deviations Grades Deviations
Nut
(Internal Thread)		 Nut Tolerance Class
Pitch Diameter
Tolerance		 Minor Diameter
Tolerance
Grades Deviations Grades Deviations

Note : * 6g is normally selected for commercial external (bolt) threads. Use this tolerance class for commercial external (bolt) threads. For usage of the other classes, refer to ISO 965-1:1998.

Note : ** 6H is normally selected for commercial internal (nut) threads. Use this tolerance class for commercial internal threads. For usage of the other classes, refer to ISO 965-1:1998.

 


RESULTS
Parameter Symbol Value Unit
Note ---
Designation -- --- ---
Tolerance Class for Bolt -- ---
Tolerance Class for Nut -- ---
Screw Thread Series -- ---
Pitch P --- mm
LIMITS OF SIZES FOR EXTERNAL THREADS (BOLTS)
Maximum Major Diameter dmax --- mm
Minimum Major Diameter dmin ---
Maximum Pitch Diameter d2max ---
Minimum Pitch Diameter d2min ---
Maximum Rounded Root
 Minor Diameter		 d3max ---
Minimum Rounded Root
 Minor Diameter		 d3min ---
Minimum Root Radii Rmin ---
Minimum Truncation Cmin ---
Maximum Truncation Cmax ---
LIMITS OF SIZES FOR INTERNAL THREADS (NUTS)
Minimum Major Diameter Dmin --- mm
Maximum Pitch Diameter D2max ---
Minimum Pitch Diameter D2min ---
Maximum Minor Diameter D1max ---
Minimum Minor Diameter D1min ---
BASIC DIMENSIONS
Basic Major Diameter d , D --- mm
Basic Pitch Diameter d2 , D2 ---
Basic Minor Diameter d1, D1 ---
Fundamental Triangle Height H ---


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

Root contour for ISO general purpose metric screw threads
ISO metric screw external thread root contour according to ISO 965-1 for positions e, f, g

Thread pitch: The distance between two adjacent threads.

List of Equations:

Parameter/Condition Symbol Equation
Height of fundamental triangle H Equation for thread height of fundamental triangle
Thread basic pitch diameter d2 , D2 Equation for thread basic pitch diameter
Thread basic minor diameter d1 , D1 Equation for thread basic minor diameter
External thread minimum truncation Cmin Equation for external thread minimum truncation
External thread maximum truncation Cmax Equation for external thread maximum truncation
External thread maximum major diameter dmax Equation for external thread maximum major diameter
External thread minimum major diameter dmin Equation for external thread minimum major diameter
External thread maximum pitch diameter d2max Equation for external thread maximum pitch diameter
External thread minimum pitch diameter d2min Equation for external thread minimum pitch diameter
External thread maximum minor diameter d3max Equation for external thread maximum minor diameter
External thread minimum minor diameter d3min Equation for external thread minimum minor diameter
Dimension y y Equation for external thread maximum minor diameter
Dimension z z Equation for external thread minimum minor diameter
Internal thread minimum major diameter Dmin Equation for internal thread minimum major diameter
Internal thread maximum pitch diameter D2max Equation for internal thread maximum pitch diameter
Internal thread minimum pitch diameter D2min Equation for internal thread minimum pitch diameter
Internal thread maximum minor diameter D1max Equation for internal thread maximum minor diameter
Internal thread minimum minor diameter D1min Equation for internal thread minimum minor diameter

List of Parameters
Symbol Definition
es, EI Fundamental deviation
Td Major diameter tolerance of external thread
Td2 Pitch diameter tolerance of external thread
TD1 Minor diameter tolerance of internal thread
TD2 Pitch diameter tolerance of internal thread

Reference:

  • Oberg, E. , Jones ,F.D. , Horton H.L. , Ryffel H.H., (2016) . Machinery's Handbook . 30th edition.  Industrial Press Inc.
  • Oberg, E. , Jones ,F.D. , Horton H.L. , Ryffel H.H., (2012) . Machinery's Handbook . 29th 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)