Square shaped shims and round shims are two common fasteners, mainly used for connecting the gap and stress distribution between bolts, nuts and connecting parts to reduce friction, limit deformation, transfer pressure and prevent air and liquid leakage.

Key differences between square and round washers:

• Shape: Square shims are in quadrilateral shape with equal side lengths and 90-degree angles; round shims are round with uniform circumferential edges.
• Application scenarios: Square shims are suitable for certain square or regular structural connections and bolt holes, mainly used for track connections such as angles, I-beams and rails; round shims are suitable for a wide range of scenarios and are more commonly used.
• Material: Both can use various metal and non-metallic materials (steel, copper, aluminium, rubber, silicone) depending on working conditions.
• Installation effect: Round washers distribute stress more uniformly; square washers may have concentrated force at corners.
• Torque control: Easier to control during installation of round washers due to uniform pressure distribution.
• Stress concentration: Square washers may experience stress concentrations at corners compared to round washers.

Etching processing is a method that removes unwanted parts with a corrosive solution, suitable for medium volume production (several hundred pieces). Etched shims are free of burrs and deformation, with high precision. The process involves:

1. Applying photoresist to the metal material and masking
2. Exposing the metal to light, sensitizing unmasked areas
3. Contacting with etchant to corrode and remove exposed metal
4. Removing residual resist, cleaning and drying

Carbon steel is a common metal material with the following advantages:

• High strength: Can withstand large external forces and pressures, widely used in construction, automotive manufacturing, and aerospace.
• Good wear resistance: Resists wear and scratches, ideal for tools, machine parts and industrial equipment.
• Strong plasticity: Easy to process and form through cold working, hot working and forging processes.
• Price economy: Relatively low production cost compared to other metal materials.

Disadvantages:

• Corrosion tendency: Susceptible to oxidation and corrosion when exposed to moisture or acidic substances.
• Low shock resistance: Poor performance in earthquake or vibration environments compared to high-strength alloys.

Galvanizing provides a rust-resistant zinc coating with various color options including silver-white, white, colored, or army green after passivation.