Pipe Taps are used to cut internal threads in parts or fittings that will be mated with threaded pipe or fittings to make a pressure tight joint. Pipe threads require higher cutting forces than regular machine thread tapping because the threads require 100% thread depth. Most threads on tapered pipe taps are cutting.
Diagram of a Pipe Tap
Essential Tips:
- Pipe taps typically have several flutes constructed in its design. They are the grooves or valleys cut into the body of the tap. Higher numbers of flutes increase the strength of the tap and reduce space or chip flow.
- Thread size is the number of Threads Per Inch (TPI) which is measured along the length of the tap. Metric sizes are referred to as thread pitch.
- Chamfers are the length of the tapering threads at the front of the tap. Both the chamfered portion of the tap and the first full thread beyond the chamfer produce the finished thread of the part.
Types of Pipe Taps:
Standard pipe taps are used for cutting internal threads in parts or fittings that will then be mated with threaded pipe or fittings to make pressure tight joint.
Extension pipe taps are used for internal deep-hole drilling of pipes and pipe fittings. They are designed with both interrupted and standard threads and are ideal for hard-to-reach-areas in general-purpose applications.
Interrupted thread pipe taps are designed with a tooth removed on each cutting edge to reduce friction and increase chip flow. They are used for general-purpose applications on both ferrous and nonferrous materials. They typically have an odd number of threads on the tap.
Spiral flute pipe taps are designed for general-purpose internal threading of pipe taps and pipe fittings. The flute geometry draws the chips away from the hole where chip disposal may be an issue. Spiral flute short projection pipe tap designs are available for shallow-hole applications.
Thread Forming pipe taps are used to form internal threads by displacing the metal without producing chips in pipes and pipe fittings. They are ideal for aluminum, brass, copper, steel and soft metals.
British standard pipe taps are used for cutting internal threads in parts or fittings. They interconnect and seal pipe ends by mating an external with an internal thread to make a pressure-tight joint.
NPT (National Pipe Taper) refers to American National Standard Taper Pipe Threads. They are commonly used for general-purpose applications and require a sealant
NPS (National Pipe Straight) refers to American National Standard Straight Pipe. They are commonly used for threads in pipe couplings.
NPSF (National Pipe Straight-Fuel) refers to Dryseal American National Standard Fuel Internal Straight Pipe Threads.
NPTF (National Pipe Taper Fuel) refers to Dryseal American National Standard Tapered Pipe Threads. They do not require a sealant due to being formed by metal-to-metal contact. They are straight internal threads and used for assembly with NPTF external threads.
BSPF (British Standard Pipe Fitting) refers to an older designation. Replaced by G series. They are used for internal or external threads where seal is not on the thread.
BSPP (British Internal Straight Parallel Pipe Threads) are commonly used for mechanical joints.
BSPRP pipe threads are used for general-purpose fastening and for mechanical assemblies. They do not meet the requirement for pipe threads where pressure-tight joints are made of threads.
BSPT (British Internal Tapered Parallel Pipe Threads) are full form threads used for pressure-tight joints.
PTF-SAE refers to short internal threads. They are used in couplings and fittings where a shorter length of engagement is required.
NPT & NPS Pipe Tap Thread Lengths Examples
| Thread Size | Thread Length (In.) |
|---|---|
| 1/16-27 | 1-1/16 |
| 1/8-27S | 3/4 |
| 1/8-27 | 3/4 |
| 1/4-18 | 1-1/16 |
| 3/18-18 | 1-1/16 |
| 1/2-14 | 1-3/8 |
| Thread Size | Thread Length (In.) |
|---|---|
| 3/4-14 | 1-3/8 |
| 1-11-1/2 | 1-3/4 |
| 1-1/4-11-1/2 | 1-3/4 |
| 1-1/2-11-1/2 | 1-3/4 |
| 2-11-1/2 | 1-3/4 |
Tap Drill Size Examples
| Thread Size | NPT Drill Size | NPS Drill Size |
|---|---|---|
| 1/16-27 | D | 1/4 |
| 1/8-27 | R | S |
| 1/4-18 | 7/16 | 29/64 |
| 3/8-18 | 37/64 | 19/32 |
| 1/2-14 | 23/32 | 47/64 |
| 3/4-14 | 59/64 | 15/16 |
| 1-11-1/2 | 1-5/32 | 1-3/16 |
| 1-1/4-11-1/2 | 1-1/2 | 1-33/64 |
| 1-1/2-11-1/2 | 1-47/64 | 1-3/4 |
| 2-11-1/2 | 2-7/32 | 2-7/32 |
Bright provides a smooth, polished finish on the tool. It increases chip flow in softer materials such as aluminum, wood and plastic.
Nitride is a thin, hard shell coating that supports surface hardness of the tool. It is commonly used where abrasive or wearing conditions exist.
Oxide, also known as black oxide or steam oxide, is a surface treatment that prevents chip building, galling and welding on the workpiece. It is commonly used on low carbons, stainless steel and ferrous metals.
Titanium Nitride (TiN) is a multi-purpose coating which increases chip flow in softer materials. The heat and hardness resistance allows the tool to run at higher speeds than uncoated tools.
Titanium Carbon Nitride (TiCN) is harder and more wear-resistant than TiN. It is commonly used on stainless steels, cast iron and aluminum alloys.
TiCN PLUS Titanium Carbon-Nitride (TiCN) plus Titanium Nitride (TiN) is all-purpose finish designed to increase tool life by two to four times more than TiN coated tools. The heat and hardness resistance allows the tool to run at higher speeds than uncoated tools.
Cobalt is harder than high speed steel and provides better wear resistance. It is commonly used on high tensile alloys.
High Speed Steel (HSS) provides good wear resistance and can be used in general-purpose applications for both ferrous and nonferrous materials.
Vanadium High Speed Steel (HSSE) is made of high speed steel, carbon, vanadium carbide and other alloys to increase abrasive wear resistance, and toughness. It is commonly used in general applications on stainless steels and high silicon aluminums.
Carbide-tips cut faster than high speed steel. It is commonly used on ferrous and nonferrous materials inclu ding cast iron, steel and steel alloys. It offers many of the advantages of solid carbide tooling at a reduced cost, especially on larger diameter tools.
Several Pipe Taps are designed with a hook, which is the entry angle of the cutting face or the part of the flute that cuts into the workpiece.
High-hook pipe taps are used on ductile materials that normally produce long continuous chips, such as aluminum, free machining stainless steel, mild steels, and plastics.
Medium hook, also known as regular hook, pipe taps produce smaller chips in general-purpose applications. They are used on a variety of ferrous and nonferrous metals.
Low-hook pipe taps are used to produce granular chips. They are used on cast iron and brass.
Extension Pipe Taps and British Standard Pipe Taps are typically constructed with a chamfer. Chamfers are the length of the tapering threads at the front of the tap. Both the chamfered portion of the tap and the first full thread beyond the chamfer produce the finished thread of the part
Plug chamfers are the most commonly used chamfer and are designed for efficiently threading through and blind holes. They have 3 to 5 chamfer threads.
Bottoming chamfers are used for threading blind holes to the bottom. They have 1 to 2 chamfer threads.
Taper chamfers are known as a starter tap. They have a longer chamfer and require a less aggressive cutting action. They are 7 to 10 chamfer threads.
Spiral Point Plug chamfers are used for general-purpose applications. They are 4 to 5 chamfer threads.