What Is a Round Countersunk Screw?
Round countersunk head screws, also known as oval head screws, feature a tapered conical shape that narrows toward the screw side, resembling a dish from the side. Unlike flat head screws, the top of a round countersunk screw head is rounded, offering a sleek appearance. They are screws with a small nominal head diameter and usually have a slotted or cross-holed drive.
The terms “round countersunk small screws” are commonly used to refer to this type of screw.
Uses of Round Countersunk Screws
Figure 1. Example of Using a Small Round Countersunk Screw
Round countersunk screws are primarily used in applications requiring female threads, where a tapered counterbore is drilled into the workpiece slightly larger than the screw’s tapered head. This allows the rounded part of the screw head to protrude slightly above the surface, providing a more aesthetic finish than flat head screws, especially in visible areas such as door closers, lock covers, and guards.
Principle of Round Countersunk Screws
Similar to other countersunk screws, round countersunk screws are designed for direct insertion into tapped female threads without the need for a nut. They are tightened using a Phillips or flat-blade screwdriver inserted into the screw head’s cross or slot. The length of these screws includes the head, differing from bolts where the length is measured excluding the head.
Types of Round Countersunk Screws
Figure 2. Types, Materials, and Shapes of Small Round Countersunk Screws
Classification of round countersunk screws includes variations in head hole shapes and materials.
1. Classification by Hole Shape of Countersunk Head
Head hole shapes include Cross (Phillips) and Suriwari (Minus), each requiring specific tools for tightening. The H (Phillips) and Z (Pozidriv) shapes differ, with Z types being less prone to cam out. The Suriwari shape, a single straight groove, uses a flat-blade screwdriver for tightening.
Figure 3. Hole and Tool Geometry of the Head of a Small Round Countersunk Screw
2. Classification by Material (Strength Classification)
Materials for round countersunk screws include steel, stainless steel, and nonferrous metals, classified by strength and governed by various standards.
Other Information on Round Countersunk Screws
- Standards such as ISO 7047 apply to round countersunk screws. Compatibility with standards is crucial for ensuring correct thread pitch and head diameter.
- Sizes range from M2 to M8, with recommended lengths from 4 to 60 mm.