I. Basic Positioning of Cross Recessed Countersunk Head Self-tapping Screws

Cross recessed countersunk head self-tapping screws are a subcategory of self-tapping screws. Their core characteristics consist of three parts:

Drive Method: The screw head is machined with a "Phillips Slot" (cross recess), which requires operation with a Phillips screwdriver/driver bit. Compared with traditional slotted (flat-head) drives, it can withstand greater torque, reduce slippage, and is suitable for automated assembly scenarios.
Thread Characteristics: Equipped with "self-tapping threads" (no pre-tapping required on the connected workpiece). It forms internal threads in materials (such as plastic, wood, and thin steel plates) through the screw’s own cutting/extruding action, simplifying the installation process.
Head Function: The core design of "countersunk head/oval countersunk head" is that the head can be embedded into the surface of the connected workpiece after installation, avoiding scratches or aesthetic issues caused by protrusion. This distinguishes it from protruding head types such as "pan head" and "cylindrical head".

II. Key Distinction: Countersunk Head vs. Oval Countersunk Head

The "flat head" and "oval countersunk head" you mentioned are essentially two different head structures. They have clear differences in appearance, post-installation state, and application scenarios, as detailed in the comparison table below:

Comparison Dimension	Countersunk Head	Oval Countersunk Head (also known as "oval countersunk head")
Head Appearance	The head has a conical bevel with a flat top (resembling a flat-top shape like an inverted funnel).	The head also has a conical bevel, but the top is a rounded arc (resembling a combination of an inverted funnel and a semi-circular top).
Post-installation State	Fully embedded in the countersink hole of the connected workpiece; the flat top of the head is flush with the workpiece surface, with no protrusion.	After being embedded in the countersink hole, the rounded top of the head will slightly protrude from the workpiece surface, forming a smooth transition.
Core Advantage	Extremely high surface flatness, suitable for scenarios requiring strict "no protrusion" (e.g., panels, decorative parts).	Balances embedment and scratch resistance; the rounded top reduces the risk of catching clothes/fingers and offers better aesthetics.
Application Scenario	Parts requiring "absolute flatness" such as furniture panels, electrical enclosures, and instrument panels.	Parts requiring both safety and aesthetics such as door and window frames, wooden structures, and daily hardware.

III. Other Core Characteristics of Cross Recessed Countersunk Head Self-tapping Screws

In addition to the head structure, the following properties of such screws also determine their application scope. Understanding these can help with selection:

Material:

Common materials include:
- Carbon steel (with zinc-plated/chrome-plated surface for rust resistance);
- Stainless steel (304/316 grades, suitable for humid environments such as kitchens and outdoors);
- Brass (suitable for decorative scenarios, such as brass furniture parts).
Thread Type:

Divided into two types:
- "Wood self-tapping threads" (with wider thread pitch, suitable for wood and plastic);
- "Metal self-tapping threads" (with denser thread pitch, suitable for thin steel plates and aluminum profiles).
  
  The thread type must match the material of the connected workpiece during selection.
Installation Requirements:
1. A "pilot hole" (with a diameter slightly smaller than the nominal diameter of the screw) must be pre-drilled in the connected workpiece to prevent material cracking;
2. Countersunk head/oval countersunk head screws require a corresponding "countersink hole" (tapered hole) to achieve the "embedding effect". The countersink angle is usually 90° (matching the conical angle of the screw head).