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Screw specification and standards summary

Professional stamping die maker in China, Changdong Tool & Die company use all kind of Level-12.9 Screws, both Metric and Inch standard.
1. Type of thread:
A: Triangular thread (60 degrees) : Bonding / locking
B: Triangular thread for pipe (55 degrees): Bonding / locking
C: trapezoidal thread (30 or 29 degrees): power transmission
D: square thread (90 degrees): power transmission
2. Common types of screws:
A: Machine Screw
B: Self-tapping screws (used in metal and used in plastic)
B-1: Sheet Metal Tapping Screw.
B-2: Plastic Tapping Screw. (for plastic, self-tapping screws)
C: Wooden Screw
D: Cement Wall Screw
3.General Screw Material
a.Low Carbon Steel
b. SS-304
c.Stainless Steel 302
d. Aluminum 5052
d. Brass
e. Bronze
f. UNS C11000 Copper
4.Common screw specifications and markings:
A: metric screw
B: US standard screw
C: inch screw
A: Metric mechanical screw:
Ex: M3 x 6 – P P B : M3 machine screw, 6mm long, cross, round flat head, black plated.
Finish Code: Appearance Processing Specifications
Head Code: Head shape
Thread Code
Screw Model Drive Code: Head section groove, feature model
Length Code: Screw length (mm)
A-1: Thread Code: Screw Model
The metric screw directly indicates the screw type with the outer diameter of the screw.
For example, M3 means the outer diameter of the screw is 3.00mm.; M4 means the outer diameter of the screw is 4.00mm.
Metric Thread Size x Pitch:
Note: The metric screw is located behind the screw model and sometimes indicates the screw pitch.such as M3x0.5, M4x0.70, M5x0.8, M6x1.
But because of the standard specification, it is usually not mentioned.
A-2: Length Code: Screw length:
Metric screw, directly indicating the length of the screw, the unit is mm.
The total length of the screw is marked, only the length below the head is calculated, and the head height is not included.
The exception is the flat head screw, the total length of the screw is marked with the head height.
A-3: Drive Code/ head section, feature.
Commonly used specifications are as follows:
a. Slotted: One word ( Minus )
b. Phillips: Cross (Plus)
c. Phil-Slot: word/cross
d. Hex Scoket: Hexagon
e. One Way: One way (only lockable, not quit)
A-4: Head Code/ Head shape.
Commonly used specifications are as follows:
a. Flat: flat head (after locking, the top is flush with the work piece)
b. Oval: Salad head
c. Round: round head
d. Pan: Round flat head
e. Truss: big round flat head
f. Hex: Hex head.
A-5: Finish Code/ Appearance Processing.
Commonly used specifications are as follows:
a. Z: Zine-Plated: galvanized
b. Ni: Ni-Plated: Nickel plating
c. Tin-Plated: Tin plating
d. Zine Plated / Green Iridite: galvanized green film treatment.
e. Radiant Plated: Multicolored
f. Passivate: Antioxidant treatment.
g. Alodial Finish: No appearance treatment
Metric self-tapping screws: directly mark the Tapping Type.
Ex: M3 x 6 –PPB, Tapping Type:
M3 self-tapping screws, 6mm long, cross, round flat head, black plated.
Generally used as a product or label, and then judged to be used in Sheet Metal or plastic parts.
B: US standard screw.
a. Generally marked with a number, such as #2-56, #4-40, #6-32, #8-32, #10-24...etc.
b. or expressed in English outer diameter,
Such as 0.086-56, 0.112-40, 0.138-32, 0.164-32, 0.190-24...etc.
Ex: 632 – 8 – P P B:
Finish Code: Appearance Processing Specifications
Head Code: Head shape
Drive Code: Head section, feature model
Length Code: Screw length
Thread Code: Screw Model
B-1: Thread Code: Screw Model
Commonly used specifications are as follows:
a. #2-56 (0.086-56): 2 Fan 56 teeth
b #4-40 (0.112-40) : 4 番 40 teeth
c. #6-32 (0.138-32) : 6 32 teeth
d. #8-32 (0.164-32) : 8 Fan 32 teeth
e. #10-24 (0.190-24): 10 Fan 24 teeth
B-2: Length Code: Screw length
The length of the US standard screw must be converted to the metric mm size.
Conversion formula: (Length Code / 32) x 25.40 = metric length mm
B-3, B-4, B-5: The marking method is the same as the metric system.

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C: Inch screw:
C-1: Thread Code:
The mark will be the denominator of 8, and then directly called the number of the molecule.
Ex: 1/8 x 0.50 –PPB: 1 split screw x 0.50” long, PPB
Ex: 5/16 x 0.50 –PPB = 2.5/8 x 0.50-PPB : 2 points half-screw x 0.50” long, PPB
Ex: 5/32 x 0.50 –PPB =1.25/8 x 0.50-PPB: 1 minute 2 PCT half screw x 0.50” long, PPB
Ex: 1/4 x 0.50-PPB= 2/8 x 0.50-PPB: 2 teeth screw x 0.50” long, PPB
Note: Sometimes it will mark coarse or fine teeth.
UNF: Fine teeth: The electronics industry is more common.
UNC: Coarse teeth: Heavy mechanical structures are more common.
Ex: 3/8 x 0.50 , UNF –PPB: 3 points fine screw x 0.50” long, PPB.
C-2: Length Code:
For the English mark, it must be multiplied by 25.40 to convert to mm

Shenzhen Changdong Stamping Dies CO., LTD. © copyright Add:NO. 56-B, Fuming South Road, Dalang, Dongguan, P.R.C 

E-mail:sales@chang-dong.com Tel:0086-769-8106 1256 0086-181-1876-8847 Sales Manager: Ms. Alice Fax:0086-769-8106 1926

Changdong is one of professional metal stamping die maker in China more than 10 years. We provide metal stamping dies to the customers in 16 countryies.
The company makes the progressive dies and transfer dies. As a stamping die manufacturer, also we provide the prototype dies and metal prototype parts for the short-run production.

Our main products: Stamping Die | Drawn Die | Metal Stampings | Checking Fixture | Progressive Die | Transfer Die | Metal Prototypes | Metal Stamping Tools| Prototype Parts | Prototype Die

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