1. What are Machine Screws?

Machine screws are tiny screws whose threads enter holes that are pre-threaded (or are used with nuts). They are usually found in machines, electronics, and equipment that require accurate components.

2. Threads – The Twist of the Screw

Types of Threads:

  • UNC / UNF: American coarse and fine threads
  • Metric (M): Prevalent in most nations
  • Special threads: Such as Whitworth, are used in particular machines

Thread Pitch:

  • Coarse: Common usage
  • Fine: Close fit in fine working

Thread Direction:

  • Right-hand (default): Right-hand threading is employed in the majority of screws
  • Left-hand: Special application (e.g., reverse thread)

3. Materials & Finishes

Materials Used:

  • Steel (Grade 2, 5, 8): General use and extremely strong
  • Stainless Steel (A2/A4): Resistant to rust, especially in damp areas
  • Brass, Aluminum, Titanium: Where corrosion resistance is needed
  • Nylon, PEEK: Non-metallic, lightweight

Surface Finishes:

  • Zinc: Rust protection
  • Black Oxide: Rust protection against light rust and suitable for a black finish
  • Nickel/Chrome: Bright, rust-protective
  • Passivation: Unique treatment of stainless steel to prevent rust

  1. Head Shapes & Screwdriver Types

Head Shapes:

  • Pan, Flat, Round, Oval, Truss, Hex, Socket Cap

Drive Types (How you turn it):

  • Slotted, Phillips, Pozidriv, Torx, Allen (hex), Square

4. Dimensions (Standard Metric & Imperial)

Size (Diameter) Thread Pitch (Metric) Thread Pitch (Imperial – TPI)
M2 (0.078″) 0.4 mm –
M3 (0.118″) 0.5 mm –
#4 (0.112″) – 40 (UNF), 28 (UNC)
#6 (0.138″) – 32 (UNF), 24 (UNC)
#8 (0.164″) – 32 (UNF), 24 (UNC)
M5 (0.197″) 0.8 mm –

6. Mechanical Properties (Steel Screws)

Grade Tensile Strength (MPa) Yield Strength (MPa) Hardness (Rockwell)
2 330 190 B70-B100
5 830 635 C25-C34
8 1170 940 C33-C39
A2 (SS) 500 210 B80-B90

7. Torque Specifications (Dry, Steel-on-Steel)

Screw Size Recommended Torque (Nm) Max Torque (Nm)
M3 0.5 – 0.9 1.2
M4 1.2 – 2.0 2.5
#6-32 0.9 – 1.4 1.8
#8-32 1.5 – 2.5 3

8. Standards (If You Need to Match Specs)

  • ISO 4762: Socket head screws
  • DIN 7985: Pan head screws
  • ANSI/ASME B18.6.3: American standard screws
  • ISO 4026: Metric socket screws

9. Where Are They Used?

  • Inside electronics like computers and phones
  • Automobile components and auto assembly
  • Heavy equipment
  • Flight and aircraft parts
  • Home appliances (televisions, microwaves, box fans)

Last Note:

There are numerous different kinds of machine screws, and the right kind to use depends on what you’re screwing them into, how much holding power it will need, and environments (like moisture or vibrations).