Screw specifications, models and standards summary

1. Type of thread:

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

1. SS-304 : Stainless Steel 304
2. SS-302: Stainless Steel 302
3. Aluminum 5052
4. Brass
5. Bronze
6. UNS C11000 Copper

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:

1. Slotted
2. Phillips:  ( Plus )
3. Phil-Slot: Minus / Plus
4. Hex Socket:
5. One Way

A-4: Head Code

General & Dimension:

1. Flat
2. Oval
3. Round
4. Pan
5. Truss
6. Hex

A-5: Finish Code

General & Dimension:

1. Z: Zine-Plated
2. Ni: Ni-Plated
3. Tin-Plated
4. Zine Plated / Green Iridite
5. Radiant Plated
6. Passivate
7. Alodial Finish

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:

1. #2-56 (0.086-56)
2. #4-40 (0.112-40)
3. #6-32 (0.138-32)
4. #8-32 (0.164-32)
5. #10-24 (0.190-24)

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