3.2.1 Metric ISO Thread

Metric Iso Thread, Dimensions according to DIN 13 Part 1-11

Representation of threads

It is important to know how threads are represented. When deriving the technical drawings from the model, the CAD system does not always display the standard elements correctly.

For threads, it always applies that touchable surfaces are drawn thicker. Therefore, the representation of external and internal threads are inverted.

Thread dimensioning:

Blind Thread

Thread Dimensioning
In order to dimension a thread according to the standard, the following specifications are necessary: the nominal diameter modified with the corresponding letter (here: M for Metric ISO thread), the core hole diameter, the length of the thread and the length of the core drill hole. The core hole diameter is usually determined by selecting a standard Screw size, but during this CAD couse it should always be stated. The length of the core hole bore, if not stated otherwise, should be 1,25 times the length of the thread, but it should also always be stated during this CAD course. The tip of the core hole automatically results from the drill's cone point

Table with examples of thread descriptions according to DIN 202 (selection)

For right-hand single-start threads:

Abbreviation	Explanation	Character in front of measurement	For threads according to DIN
M 20	Metric ISO thread with 20mm outer diameter	M	13 Teil 1
M 80 x 2	Metric ISO fine thread with 80 mm outer diameter and 2 mm gradient	M	13 Teile 2...12
G 1 1/2	Cylindrical pipe thread for connections without sealing threads	G	ISO 228
Tr 40 x 7	ISO metric trapezoidal thread with 40 mm outer diameter and 7 mm gradient	Tr	103 Teil 2
S 48 x 8	Sawtooth-thread with 48 mm outer diameter and 8 mm gradient	S	513 Teil 2

ATTENTION: Thread and screw designations can lead to misunderstandings! For screws, the value after the' x' indicates the length (M8 x 20 = 20mm long)! For a thread, the value after the' x' indicates the gradient of the thread!

For left-hand and multi-start threads:
The additional description is valid for metric, trapezoidal and saw threads.

Abbreviation	Explanation of the additional designation
M 60-LH Tr 32 x 6-LH	Left-hand thread with abbreviation LH behind the thread designation
Tr 48 x 6 (P 3)	Righthand double thread The number of turns of a thread is calculated from the gradient Ph divided by the division P. Here: P=6:3=2

The individual diameters and other important markings for thread representation are listed below:

Nominal Diameter	d = D
Gradient	P
Thread depth of the bolt thread	h₃ = 0,6134·P
Thread depth of nut thread	H₁ = 0,5413·P
Curves	R = 0,1443·P
Pitch Diameter	d₂ = D₂ = d-0,6495·P
Core diameter of the bolt thread	d₃ = d-1,22687·P
Core diameter of the nut thread	D₁ = d-2·H₁
Flancangle	60°
Stress cross-section	π/4·(d₂+d₃)/2)²

Norm

Please refer to the corresponding values in "DIN 13 Part 1: Metric ISO thread". You can access it via the Nautos portal (see 3.1 Access to Standards).