Tap  Guide

Styles | Chamfer | Markings | Symbols | Thread Forms


Tap Style Guide

Hand Tap

These standard style taps have straight flutes of a number specified as either standard or optional. Hand taps are for general purpose applications such as production tapping or hand tapping operations. Taper, plug and bottoming styles provide versatility in tough materials, blind and through holes.

Spiral Point Tap

As to general physical dimensions, spiral point taps are identical with the standard hand tap. However, the spiral point tap has the cutting face of the first few threads cut at a pre-determined angle relative to the tap's axis angle to force the evacuation of chips ahead of the cutting action. This feature, plus the excellent shearing action of the flute, make spiral pointed taps ideal for production tapping of through holes. Typically, this type of tap has a shallower flute passage than conventional taps. This gives the spiral point tap more cross-sectional area, which means greater strength, allows higher tapping speeds, and requires less power to drive.

Regular or Slow Spiral Tap
Regular (or slow) Spiral

Fast Spiral Tap
Fast Spiral

These taps, as the name implies, are made with spiral flutes instead of straight flutes. This spiral fluting feature aids in drawing chips out of a hole, or serves to bridge a gap inside the hole such as a keyway or cross-hole. Commonly available in slow spiral (25-30¡ helix angle) or fast spiral (45-60¡).

Interrupted Thread Tap

These taps have an odd number of lands with alternate teeth in the thread helix removed. The removal of every other tooth helps to break the chip and allows a greater supply of lubrication to reach the cutting teeth, reducing the incidence of torn threads. Ideal for tapping non ferrous metals and low carbon steel; as well as use in titanium and high hardness alloys.

Thread Forming Tap (TRU-FLO®)

These taps are fluteless except as optionally designed with one or more lubrication grooves. The thread form is lobed so there is a finite number of points contacting the work. This tap does not cut, so it is 'chipless', and consequently will not cause a chip problem. The tool forms the thread by extrusion, thus thread size can be closely maintained. The fluteless design allows high quality threads, faster tapping speeds, higher production, and generates no chips which simplifies tapping of blind bottoming holes (threads can be formed the full depth of the hole).

Straight Pipe Tap
Straight Pipe Tap

Taper Pipe Tap
Taper Pipe Tap

These taps are for producing standard straight or tapered pipe threads in a wide range of pipe connections. Manufactured with the appropriate design variations to cut specified pipe thread forms.

Combined Drill & Tap (Cost Cutter")

This high production tool is specially designed to drill and tap in one pass only. By design, this value-added tool reduces machining operations and subsequent parts handling. The drill end features a self-centering helical point, and the tool shank and square fit standard tap holders.

ACME Thread Tap

Acme screw threads were devised to allow rotary and transversing motion on machines; and are also used in jacks, valves, presses and other mechanisms where heavy loads are encountered. The acme thread is characterized by a 29° included angle. Acme taps typically require specialized engineering and design due to the nature and severity of cut required in producing Acme threads.

how to order acme taps



ACME Thread Tap

Trapezoidal screw threads were devised to allow rotary and transversing motion on machines; and are also used in jacks, valves, presses and other mechanisms where heavy loads are encountered. The trapezoidal thread is characterized by a 30° included angle. Trapezoidal taps typically require specialized engineering and design due to the nature and severity of cut required in producing trapezoidal threads.

( these are the metric equivalent of Acme Taps but with a 30° included angle )

how to order trapezoidal taps

Tandem ACME Tap

These taps combine the initial roughing cut with the final finishing cut, in one pass, to achieve an acme screw thread. These taps are economical and enhance production levels by saving on the operation of two tools. Since acme thread pitches are generally coarse relative to diameters, these taps are subjected to heavy chip loads. To achieve a high quality acme thread in a cost-effective manner, roughing and finishing operations are recommended.

EXTENSION TAPS (Incl. Nut & Pulley Taps)

Extension Tap

These taps are made to conventional tap dimensions, except that they have an extended shank to reach inaccessible holes. Thread length, shank diameter, and shank square are made to standard specifications listed in Table 302. Extension taps are available in both hand and spiral point styles, and in small shank style.

Pulley Tap

The hub portion of pulley parts contain oil cups and set screw holes, most of which cannot be reached with ordinary hand taps. Pulley taps have the same basic thread dimensions as hand taps, but pulley taps differ in that they have a longer shank which is of the same basic major diameter as the threaded portion. When tapping pulley hub holes, the taps are inserted through holes in the rims which are slightly larger than the shanks of the taps. These holes serve as guides or bushings for the taps to assure proper alignment when tapping. Pulley taps can also be used for general tapping in parts where an extra long length is required to reach the holes being tapped.

Nut Tap

Nut taps feature a long chamfer which assists in entering the drilled hole, and distributes the cutting action over several teeth. These taps were initially designed for tapping nuts and have a long thread length. The shank diameter is smaller than the tap's minor diameter to allow the accumulation of several nuts after tapping. Nut taps also feature an extended square length.

Solid Carbide Tap

These taps allow higher metal removal rates through higher speeds, which are possible through the micrograin structure of carbide. Users will also benefit from a dramatic increase in tap life, less downtime, fewer tool changes, and consistent high quality thread finishes.

CARB-I-SERT Insert Tap

These taps are an economical alternative to solid carbide taps, especially in larger diameter tools. Solid carbide cutting face inserts are brazed to a H.S.S. tap body, then threaded to exacting specifications. Carbide cutting teeth allow higher performance and production.






Chamfers for Thread Cutting Taps ( taper, plug, bottoming )

Chamfers for Thread Cutting Taps ( taper, plug, bottoming )

The tap chamfer is the tapering of the threads to distribute cutting action over several teeth. The type of hole to be tapped has much to do with the chamfer style of that tap that's best suited. Some holes go all the way through; some, while not through-holes, are relatively deep; some are quite shallow (a little deeper than diameter). Each of these three kinds of holes - through, deep-bottoming blind, and shallow bottoming - has a tap chamfer best suited to threading requirements.

Taper Tap Image

Taper Taps - This style, with a 8-10 thread chamfer, has the longest chamfer of the three to distribute action over the maximum number of teeth; and the taper also acts as a guide in starting the cutting action in the hole. Taper style taps start the thread square with the workpiece. Taper taps are commonly used in through holes and in materials where a tapered guide is necessary.

Plug Tap Image

Plug Taps ( Seconding Tap)- This style, with a 4-6 thread chamfer, is most widely used in through holes and where there is sufficient room at the bottom in blind holes.

Bottom Tap Image

Bottoming Taps ( Finishing Tap) - This style, with a 1-2 thread chamfer, is made with just enough chamfer for starting in the hole; as the name implies, it is designed to thread blind holes to the bottom.


Standard System of Tap Marking

Standard System of Tap Marking

Taps, dies and other types of threading tools are marked according to the Standard System of Marking Ground Thread Taps. Tools are marked with the nominal size, number of threads per inch (pitch), and the appropriate thread form symbol and pitch diameter symbol. Symbols typically used are listed.

Tap Marking Image

Pitch Diameter Limit Symbols

All standard ground thread taps are marked with the letter "G" to designate Ground Thread. The letter G will be followed by the letter "H" to designate above basic; or the letter "L" to designate below basic. The number following H or L signifies the number of .0005" steps above or below the basic pitch diameter.

For instance, the tap pictured above is a 3/8" dia. tap with 20 threads per inch (pitch), and has a NS (American National Special Thread) thread form. The tap is made from High Speed Steel, and the GH-3 pitch diameter limit symbol indicates a Ground Thread tap with pitch diameter limits .0010 to .0015 over basic.

Pitch Diameter Limits for taps to 1" diameter inclusive:

L1 = Basic to Basic minus .0005
H1 = Basic to Basic plus .0005
H2 = Basic plus .0005 to Basic plus .0010
H3 = Basic plus .0010 to Basic plus .0015
H4 = Basic plus .0015 to Basic plus .0020
H5 = Basic plus .0020 to Basic plus .0025
H6 = Basic plus .0025 to Basic plus .0030

Taps larger than 1" dia. are ground to a .0010" tolerance on the pitch diameter and are, for example,

H4 (Basic plus .0010" to Basic plus .0020").


Thread Form Symbols

ACME-C Acme Thread-Centralizing
ACME-G Acme Thread-General Purpose
AMO American Standard Microscope Objective Thread
ANPT Aeronautical National Form Taper Pipe Thread
(Ground thread tap marked NPT)
BA British Association Standard Thread
BSF British Standard Fine Thread Series
BSP British Standard Pipe (Parallel) Thread
BSSPI British Standard Pipe (Parallel) Thread
BSPF British Standard Pipe (Parallel) Thread
BSPG British Standard Pipe (Parallel) Thread
BSPP British Standard Pipe (Parallel) Thread
BSPT British Standard Taper Pipe Thread
BSPTr British Standard Taper Pipe Thread
BSPT British Standard Taper Pipe Thread
BSW British Standard Whitworth Coarse Thread Series
G British Standard Pipe (Parallel) Thread
KR British Standard Taper Pipe Thread
M Metric ScrewThread Series
N American National 8, 12 and 16 Thread Series (8N, 12N, 16N)
N BUTT American Buttress Screw Thread
NC American National Coarse Thread Series
NEF American National Extra Fine Thread Series
NF American National Fine Thread Series
NGO National Gas Outlet Thread
NGT National Gas Taper Thread (see "SGT")
NH American National Hose Coupling and Fire Hose Coupling Threads
NPS For tap marking only (See NPSC, NPSM)
NPSC American National Standard Straight Pipe Thread in Pipe Couplings (Tap marked NPS)
NPSF Dryseal American National Standard Fuel Internal Straight Pipe Thread
NPSH American National Standard Straight Pipe Thread for Hose Couplings
NPSI Dryseal American National Standard Intermediate Internal Straight Pipe Thread
NPSL American National Standard Straight Pipe Thread for Loose Fitting Mechanical Joints with Locknuts
NPSM American National Standard Straight Pipe Threads for Free-Fitting Mechanical Joints for Fixtures (Tap marked NPS)
NPT American National Standard Taper Pipe Thread (See ANPT, NPTR)
NPTF Dryseal American National Standard Taper Pipe Thread
NPTR American National Standard Taper Pipe Thread for Railing Joints (Tap marked NPT)
NS American National Thread-Special
PS British Standard Pipe (Parallel) Thread
PT British Standard Taper Pipe Thread
PTF Dryseal SAE Short Taper Pipe Thread
R British Standard Pipe (Parallel) Thread
British Standard Taper Pipe Thread
SGT Special Gas Taper Thread
SPL-PTF Dryseal Special Taper Pipe Thread
STI Special Thread for Helical Coil Wire Screw Thread Inserts
Stub Acme Stub Acme Thread
*UN Unified Constant Pitch Thread Series
*UNC Unified Coarse Thread Series
*UNEF Unified Extra Fine Thread Series
*UNF Unified Fine Thread Series
UNJ Unified Thread Series with a 0.15011P to 0.18042P Controlled Root Radius on External Thread only.
UNJC Unified Coarse Thread Series with a 0.15011P to 0.18042P Controlled Root Radius on External Thread only.
UNJF Unified Fine Thread Series with a 0.15011P to 0.18042P Controlled Root Radius on External Thread only.
UNM Unified Miniature Thread Series
UNR Unified Constant Pitch Thread Series with a 0.108P to 0.144P Controlled Root Radius; Ext. thread only.
UNRC Unified Coarse Thread Series with a 0.108P to 0.144P Controlled Root Radius; Ext. thread only.
UNRF Unified Fine Thread Series with a 0.108P to 0.144P Controlled Root Radius; External thread only.
*UNS Unified Thread-Special
V A 60¡ "V" thread with Truncated Crest and Root. The theoretical "V" Form is usually flatted to the user's specifications.
WHIT British Standard Whitworth Special Thread

*Taps are not marked with "U" but with the symbol for the corresponding American Standard thread form with which it is compatible.

link to tap index page

Trademarks are the properties of their respective owner(s).

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