The four characters 'Gui Wu Gui' are distinct. Memorizing and distinguishing them by their shapes alone might be challenging, but understanding the structure of Chinese characters makes it much easier to differentiate them. Today, I won't delve into language here; instead, I want to discuss how many similar things can be easily distinguished by identifying their origins and roots, leading to practical differences in application. Internal threads are a crucial element in many mechanical connections, providing essential conditions for the use of fasteners such as bolts, nuts, and studs. Internal threads are typically created using specialized tapping tools, such as the following:

They vary in size, shape, and function. The tap usually clearly indicates the thread specifications, such as 0.250-20 UNC-2A. This format is concise, with no extra letters or numbers. "0.250-20" represents the basic thread size, indicating the nominal diameter and number of threads per inch after tapping. "UNC" stands for the type of pre-threaded thread, commonly UN, UNC, or UNJC. The tap also specifies its material, such as high-speed steel, hard alloy steel, or other hard materials suitable for tapping. The choice depends on the material being tapped and the required thread accuracy. For example, hard alloy steel can be used to tap stainless steel and titanium alloys, whereas high-speed steel performs poorly in these materials. In terms of types, there are three common types of manual taps: flat-bottom taps have almost no taper, making them ideal for tapping blind holes, ensuring a minimal thread finish at the bottom of the hole.

Plug Tap (CS) A tap with a conical cutting edge in the middle of the tap helps the tap align into an unthreaded hole and is suitable for most applications.

The cutting edge of the conical tap is also conical, similar to a plug tap, but with a greater and more pronounced taper, used for holes that require higher precision and are more difficult.

Sometimes, to achieve better hole quality, multiple taps are used simultaneously. When tapping on softer materials like aluminum alloy, medium taps are typically used; if tapping blind holes, switch to flat-bottomed taps as you approach the bottom of the blind hole to continue cutting. For hard materials, taps with a larger taper can be chosen, which effectively reduces the torque required for threading. In fact, fastener knowledge isn't difficult; it's just that there are too many similar products, each with its own unique characteristics. A closer look at the commonalities and differences between various products can help avoid being 'only seeing the mountain from within.'