Hand Tap set of 3 pieces ISO 529 HSS-G - NPT 3/8 x 18

This hand tap set is ideal for:

• General Use: In the workshop, for pipe installations, and industrial applications.
• Materials: Well-machinable materials up to 900 N/mm², such as unalloyed and low-alloy steels.
• Holes: For cutting threads in through holes and blind holes.
• Usage Type: Optimized for manual and machine use, which makes it particularly versatile.

The set consists of three perfectly coordinated taps, each cutting a part of the thread. As NPT threads are tapered, the thread depth is built up step-by-step to achieve a clean and tight result.

NPT stands for "National Pipe Taper" and designates an American tapered pipe thread according to the standard ANSI/ASME B1.20.1. Unlike straight threads that require a sealant, an NPT thread creates its seal through the wedging of the conical flanks.

The taper of 1:16 is the decisive characteristic of this thread. It means that the diameter of the thread tapers by 1 mm per 16 mm of thread length. This ensures a self-sealing connection, as the thread wedges tightly into the mating part when screwed in, preventing leaks.

The designation NPT 3/8 x 18 means:

• Nominal Size 3/8: The nominal size for the pipe thread in inches. It does not refer to the actual outer diameter, but to the inner pipe size.
• 18: The number of threads per inch.

The ISO 529 standard standardizes the dimensions of the threading tool itself, such as the overall length and shank diameter. This ensures that the NPT thread cutter is compatible with common tool holders and tap wrenches.

For an optimal result, follow these steps:

1. Prepare the Hole: Pre-drill the core hole with the correct diameter of 14.3 mm. Deburr the hole to ensure a clean start.
2. Clamp and Align: Take the taper tap (first tap in the set) and clamp it securely in a suitable tap wrench or in a threading machine. Place the tap perpendicularly on the hole.
3. Cut the Thread: Apply light, even pressure and turn the tap clockwise. After every half turn, turn back a quarter turn to break the chips and facilitate the cutting process.
4. Lubrication: Use a suitable cutting oil throughout the process to reduce friction and extend the life of the tool.
5. Change Taps Step-by-Step: Switch successively to the second and bottoming taps and repeat the cutting process until the thread is cut to its full depth.

1. What is the main difference between an NPT thread and a metric thread?

The main difference lies in the profile and sealing. A metric thread (M) is cylindrical and requires a sealant (e.g., O-ring or sealant compound) to be fluid-tight. An NPT thread is conical (tapered) and seals itself by the wedging of the thread flanks.

2. Why is a 3-piece set used for NPT threads?

Although many NPT taps are sold as single-piece tools, a 3-piece set allows for a gradual cutting of the conical thread. This reduces the load on the tap, ensures better chip evacuation, and leads to a cleaner and more precise result, especially in tough materials.

3. What core hole diameter do I need for NPT 3/8 x 18?

According to the product specifications, the recommended core hole diameter for this thread is 14.3 mm. It is crucial to maintain this value precisely to cut a correct thread and ensure a tight seal.

4. What is the difference between manual and machine use?

This versatile NPT tap can be used manually with a tap wrench or in a threading machine. For manual use, the power transmission is purely manual, while a machine ensures a consistent rotational speed and feed rate, which is advantageous for series production.

5. What role does the 1:16 taper play?

The taper is the most important characteristic of the NPT thread. It ensures that the thread seals itself when screwed in. The tighter the connection is, the more the flanks wedge into each other, allowing for a leak-free connection without additional sealants (although these are often used).