# ROUGH CALCULATION OF METRIC BOLT SIZE

Bolted joint is a type of joint where minimum two parts are connected to each other with a bolt. Main functions of a bolted joint are keeping parts together during service life and transmitting torque, moment and force between parts. Bolt sizing is very critical issue and improper design of a joint can lead failures.

Metric bolt size calculator roughly determines bolt diameter in a bolted joint according to guideline VDI 2230 Part-1 , which was prepared by the Association of German Engineers (VDI), and treats the calculation of concentrically and eccentrically clamped bolted joints.

This calculator can be used for initial sizing of a bolt and preload in a joint according to metric unit system. The tool is applicable for:

• Bolt dimension range from M3 to M39
• Bolt strength grades of G8.8, G10.9 and G12.9

• A sample example about bolt sizing for pressure vessel cap is given in  "Examples" section of this page to show usage of the calculation tool. Reference information on friction coefficients, load introduction factor and loading types are given in "Supplements" section to assist the usage of the calculator.

This calculator can be used to roughly estimate bolt diameter for a joint but more detailed calculation shall be done according to VDI 2230 Part-1 guideline.

### Metric Bolt Sizing Calculator:

 INPUT PARAMETERS Parameter Value Axial Load [FA] N Transverse Load [FQ] Min. friction coef. between clamped parts [μ]+ - Axial load type and introduction location * Static and concentric Dynamic and concentric Static and eccentric Dynamic and eccentric Tightening technique Simple tightening spindle Torque wrench Angle control Bolt Strength Grade G8.8 G10.9 G12.9

Note 1 : +Minimum values for static friction coefficients between materials which are used in general engineering application. Reference values are given in  "Supplements" section.

Note 2 : *Graphical representation of axial loading types which is given to assist selection of loading type among the alternatives is given in "Supplements" section.

 RESULTS Parameter Value Required preload FMmax ---- N Required bolt size for selected grade ---- ---

Note 1 : This calculator is applicable for bolt dimension range from M3 to M39 and for strength grades G8.8 , G10.9,  G12.9.

Note 2 : Use dot "." as decimal separator.

### Definitions:

Axial load: Load parallel to bolt axis. Axial load can be concentric (along the bolt axis) or eccentric.

Bolt strength grade: Strength grade that shows tensile and yield strength of a bolt.

Preload: The tension load created in a fastener when it's tightened. This tension load presses clamped parts together. Preload must be large enough to prevent joint failure.

### General Information:

Calculation methodology of the calculator is summarized below. [Reference-1]

Note: Increase 1 step means, getting the value which is next row under the current value. For example if current value is 1000 N, 1 step increase will result 1600 N.