What Are The Advantages Flange Head SEMS Screws? Part Two — Gorun Screw

Why flange head Screws Outperform Conventional Screws + Separate Washers

Let’s examine the key advantages flange head screw design compared to traditional screw-and-washer combinations:

1. 

Eliminates Washer Deformation Under Load
Standard washers are typically softer than the fasteners they accompany. Under high stress, they can undergo plastic deformation against the harder screw head, leading to loss of clamp load. In contrast, the flange of a flange head screw shares the same material hardness as the screw body, maintaining structural integrity and consistent clamping force.

2. 

Prevents Eccentric Loading and Stress Concentration
Research shows that the clearance hole in conventional washers can cause eccentric loading, resulting in extremely high localized stress.
To reduce the risk of head-to-shank fracture, screws feature a fillet radius (a smooth transition arc) beneath the head. This requires washers to have a larger inner diameter to accommodate the fillet—partly for easier assembly. However, this clearance can cause the washer to shift off-center during tightening, leading to uneven load distribution, surface indentation, joint damage, and significantly lower actual clamp force than theoretically expected.

3. 

Reduces Embedment Losses
Even seemingly flat surfaces are microscopically rough. As shown in microscopic images of zinc-plated washers (see illustration below), actual contact occurs only at the peaks of surface asperities.
When a separate washer is used, two additional interfaces are introduced: one between the screw head and washer, and another between the washer and the workpiece. Each interface is subject to embedment—the localized plastic flattening of surface roughness under load. With two surfaces undergoing embedment simultaneously, total clamp load loss increases substantially.
Flanged screws eliminate this issue by removing the extra interface, thereby preserving more of the intended preload.

In summary, these factors explain why flange head screw designs offer greater reliability than assemblies using separate washers.

That said, it’s important to note that specialty washers—such as spring lock washers, EPDM rubber sealing washers, or PVC protective washers—still play essential roles where specific functions like vibration resistance, waterproofing, or surface protection are required. The existence of flange head screws doesn’t negate the value of these purpose-built, separate washers.

To further enhance on-site efficiency for our customers, Gorun Screw not only supplies high-quality flange head SEMS screws, but also offers matched specialty washers upon request. For example, when you purchase our premium self-tapping or self-drilling screws, we can simultaneously provide large-dome (umbrella-type) EPDM sealing washers specifically designed for COLORBOND corrugated roofing applications.

If you have any related needs, please feel free to contact Gorun Screw at any time!