What Is a Threaded Hole?
A threaded hole is a hole with internal threads that allow a screw, bolt, or threaded fastener to be securely installed. Internal threads are typically produced after drilling by tapping, thread milling, or other specialized machining processes.

Threaded holes eliminate the need for additional fastening hardware in many assemblies while providing a compact and reusable connection. They are widely used in mechanical structures where components must be assembled, disassembled, or maintained throughout their service life.

The design of a threaded hole should consider not only the required fastening strength but also the manufacturing process and the material being machined.

Common Types of Threaded Holes
Different applications require different threaded hole configurations. Selecting the appropriate type improves assembly efficiency and ensures the connection performs as intended.

Through Threaded Holes
A through threaded hole extends completely through the workpiece, allowing chips to exit during machining and making tapping relatively simple.

Because chips are easily evacuated, through holes generally reduce the risk of tap breakage and provide faster machining. They are commonly used in brackets, mounting plates, structural components, and other applications where access from both sides is available.

Blind Threaded Holes
Blind threaded holes do not pass through the entire workpiece. Instead, they terminate at a specified depth, making them suitable when the opposite side of the component must remain intact.

Although widely used, blind holes require greater machining accuracy. Chips tend to accumulate at the bottom of the hole, increasing the difficulty of tapping and requiring careful control of thread depth. Designers should also provide sufficient clearance below the threads to accommodate the tap and remaining chips.

Tapered Threaded Holes
Tapered threads gradually decrease in diameter along their length, creating a tight mechanical seal as the mating thread is installed.

These threaded holes are commonly used in piping systems, hydraulic equipment, and pneumatic fittings where leakage prevention is critical. The tapered profile allows the threads themselves to create the sealing force without relying solely on additional sealing components.

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Threaded Inserts
In some materials, especially aluminum, plastics, and other relatively soft metals, threaded inserts are used to improve thread strength and wear resistance.

Rather than machining threads directly into the base material, an insert containing hardened internal threads is installed after machining. This approach increases durability and allows repeated assembly without damaging the surrounding material.

Threaded inserts are frequently used in aerospace components, electronic enclosures, and products that require frequent maintenance.

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