1. What is a combination screw?

A combination screw, also known as a SEMS screw or pre-assembled screw, is a fastener that comes with a washer already fitted onto the screw shaft before delivery. The washer is permanently retained under the screw head and cannot fall off.

This simple but clever design saves assembly time and prevents lost washers – a common frustration in traditional screw + separate washer combinations.

2. Why is a pre-assembled washer needed?

In many mechanical and electronic products, a washer is required under the screw head to distribute pressure, prevent loosening, or protect the surface. With separate parts, workers must pick up a screw and a washer and assemble them manually – which is slow and easy to make mistakes.

The combination screw solves this by keeping the washer captive. The washer rotates freely but cannot be removed. This allows high-speed automated assembly using power tools, reduces handling steps, and eliminates the risk of missing washers.

3.Common Types of Combination Screws

Combination screws come in many variations depending on the washer type and drive style. Common washer types include:

• Spring washer – provides anti-vibration tension

• Flat washer – increases bearing surface and protects material

• Toothed lock washer – bites into the surface for extra grip

Drive styles can be Phillips (cross), hex socket, Torx, slotted, etc. Taiyuanfeng offers customization of all these parameters.

4. Common Materials and Surface Treatments

To suit different environments, combination screws are available in various materials:

• Carbon steel (grades 4.8, 8.8) – good strength for general industrial use

• Stainless steel (SS304, SS316) – corrosion resistance for outdoor or humid conditions

Surface treatments such as zinc plating (blue, white, yellow, black), hot-dip galvanizing, or Dacromet provide additional rust protection.

5. Typical Industries

Combination screws are widely used in:

• Electronics – securing PCBs, power supplies, and casings where missing washers could cause shorts

• Furniture (RTA) – ready-to-assemble furniture kits benefit from fewer loose parts

• Automotive interior – trim panels, plastic parts, and dashboard assemblies

• Home appliances – washing machines, air conditioners, and kitchen equipment

6. Quality and Standards

Reputable manufacturers follow international standards such as DIN 6900 or ISO 10510 to ensure consistent dimensions and performance. Taiyuanfeng performs torque testing and washer retention checks on each batch to guarantee reliability.

For buyers, using combination screws reduces inventory complexity (one SKU instead of two) and lowers the risk of field failures caused by missing washers.

Taiyuanfeng supplies standard and custom combination screws for global buyers. Free samples available for qualified businesses. OEM logo engraving supported for large orders.