When using bolts or processing bolts, we need to calculate certain values through thread formulas. So what calculation formulas do you know for threads? In this article, TorcStark will introduce 8 thread formula algorithms and help you better understand these formulas by adding practical calculation cases.

Now, let’s get started! The following calculation formulas are all international standards.

I. Calculation formula for inner hole diameter of thread extrusion tapping:

Formula: tooth outer diameter – 1/2 × tooth pitch

Example 1:


Example 2:


II. Conversion formula for general British wire tapping:

1 inch = 25.4mm

Example 1: (1/4-30)

1/4×25.4=6.35(tooth diameter)

25.4÷30=0.846 (tooth distance)

Then 1/4-30 converted into metric teeth should be: M6.35×0.846

Example 2: (3/16-32)

3/16×25.4=4.76 (tooth diameter)

25.4÷32=0.79 (tooth distance)

Then 3/16-32 converted into metric teeth should be: M4.76×0.79

III. The general formula for converting imperial teeth into metric teeth:

Numerator/denominator × 25.4 = tooth outer diameter

Example 1: (3/8-24)

3÷8×25.4=9.525(tooth outer diameter)

25.4÷24=1.058 (metric pitch)

Then 3/8-24 converted into metric teeth should be: M9.525×1.058

IV. Formula for converting American teeth to metric teeth:

Example: 6-32

6-32 (0.06+0.013)/code×6=0.138

0.138×25.4=3.505 (outer diameter of tooth)

25.4÷32=0.635 (tooth distance)

Then 6-32 converted into metric teeth should be: M3.505×0.635

1. Hole inner diameter calculation formula:

The outer diameter of the tooth – 1/2 × the tooth pitch should be:


Then the inner diameter of 6-32 should be 3.19

2. Extrusion wire tapping inner hole algorithm:

Simple calculation formula of lower hole diameter 1:

Tooth outer diameter – (tooth pitch × 0.4250.475)/code = lower hole diameter

Example 1: M6×1.0

M6-(1.0×0.425)=5.575 (maximum lower aperture)


Example 2: Simple calculation formula for the inner diameter of the hole tapped by the cutting wire:

M6-(1.0×0.85)=5.15 (maximum)


M6-(Tooth pitch×0.860.96)/code=lower aperture

Example 3: M6×1.0=6-1.0=5.0+0.05=5.05

V. Simple formula for calculating the outer diameter of the press teeth:


The lower limit of the allowable deviation of the aperture can be passed.
The upper limit of the allowable deviation of the hole diameter cannot be passed.

Example 1:

M3×0.5=3-0.01×0.645×0.5=2.58 (outer diameter)

Example 2:

M6×1.0=6-0.1×0.645×1.0=5.25 (outer diameter)

VI. Calculation formula for metric tooth rolling diameter: (Full tooth calculation)

Example 1:

M3×0.5=3-0.6495×0.5=2.68 (outer diameter before turning)

Example 2:

M6×1.0=6-0.6495×1.0=5.35 (outer diameter before turning)

VII. Embossed outer diameter depth (outer diameter)

Outer diameter÷25.4×Tooth pitch=Outer diameter before embossing

Example: 4.1÷25.4×0.8 (tooth pitch)=0.13

Embossing depth should be 0.13

VIII. Diagonal conversion formula for polygonal materials:

Formula 1:

1. Square: Diameter of opposite sides × 1.414 = Diameter of opposite corners

2. Pentagon: Diameter of opposite sides × 1.2361 = Diameter of opposite corners

3. Hexagon: Diameter of opposite sides × 1.1547 = Diameter of opposite corners

Formula 2:

1. Four corners: Diameter of opposite sides ÷ 0.71 = Diameter of opposite corners

2. Hexagonal: Diameter of opposite sides ÷ 0.866 = Diameter of opposite corners

IX. Finally

The above is the specific content of the 8-thread formula algorithms. The content is relatively concise and requires you to have some basic knowledge. You can check our other articles to learn about other bolt knowledge. Please leave your questions in the comment area if you have any questions.