Screw specifications, models and standards summary
A: Triangle thread (60 degrees) : bonding/locking
B: Triangle thread (55 degrees): joint/lock
C: Trapezoidal thread (30 or 29 degrees) : Power drive
D: Square thread (90 degrees) : Power drive
Ii. Common screw types:
A: Machine Screw
B: Tapping Screw: (for metal and plastic)
B-1: Sheet Metal Tapping Screw.
B-2: Plastic Tapping Screw.
C: Wooden Screw
D: Drywall Screw
Iii. Common screw material:
a.Low Carbon Steel
Iv. Common screw specifications and Marks:
A: Metric screws
B: American gauge screw
C: English screw
A: Metric mechanical screw: Metric
Ex: M3 x 6 – P P B : M3 mechanical screw, 6mm long, Plus, round flat head, black coating.
Finish Code
Head Code
Thread Code
Model:
Drive Code
Length Code
A-1: Thread Code
Metric screws directly mark the screw type with the outside diameter of the screw
M4 means the outside diameter of the screw is 3.00mm.
M4 means the outside diameter of the screw is 4.00mm.
Metric Thread Size x Pitch:
Note: The metric screw is set behind the screw type, and the pitch of the screw is sometimes marked.
For example, M3x0.5 , M4x0.70, M5x0.8 , M6x1.
But because of the standard specification, it is usually not mentioned.
A-2: Length Code
Metric screw, direct marking screw length, unit is mm.
The total length of screws is indicated. Only the length below the head is calculated, not including the height of the head.
Except for flat head screws, the total length of the screws is indicated including the height of the head.
A-3: Drive Code
Commonly used specifications are as follows:
A-4: Head Code
General & Dimension:
A-5: Finish Code
General & Dimension:
Tapping Type.
Ex: M3 x 6 –PPB, Tapping Type:
M3 self-tapping screw, 6mm long, +, d. Pan, black coating.
Generally, it is used as Sheet Metal or plastic parts by product identification or labeling.
B: The US System Screw.
a.Usually marked with a model, such as #2-56, #4-40, #6-32, #8-32, #10-24…etc.
b.Or in inch 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
Head Code
Drive Code
Length Code
Thread Code
B-1: Thread Code
General & Dimension:
B-2: Length Code:
the length of the screw must be converted to the metric mm size.
Formula: (Length Code / 32) x 25.40 = The length of the metric system mm
B-3, B-4,B-5 : The marking method is the same as the metric system
C: Inch system
Thread Code
Mark the denominator as 8, then directly call the numerator number.
Ex: 1/8 x 0.50 –PPB
Ex: 5/16 x 0.50 –PPB = 2.5/8 x 0.50-PPB
Ex: 5/32 x 0.50 –PPB =1.25/8 x 0.50-PPB
Ex: 1/4 x 0.50-PPB= 2/8 x 0.50-PPB
Note: Thick or thin threaded are sometimes marked.
UNF: Thin threaded: more commonly used in electronics.
UNC: Thick threaded: heavy mechanical structure is more commonly used.
Ex: 3/8 x 0.50 ,UNF –PPB