Tapping Threads & Associated Reference Tables
Last updated on Saturday, April 20, 2013 06:54:19 AM Eastern US Time Zone

Hand Tappers, Tap Handles, Cutting Fluids, Tap Guides, Tapmatic 30X, Die Holders,
Drill-Tap Sets, Drill-Tap Chart, Thread Measurement, Bolt Head Grade Identification

Introduction to Taps   Single-point threading Section   How to Drill a Hole   Hand Tapper Manual
National Unified Coarse & Fine Thread Dimensions with Tap Drill Sizes   Standard Acme Screw Thread Dimensions
ISO External Threads   Double Depth of Screw Threads   Standard Pipe Thread & Tap Drill Sizes
Tap Drill Sizes for Fractional Size Threads   mm Tap Drill Sizes   Decimal Equivalents of Number Size Drills
Metric & Inch Equivalents   Decimal Equivalents of Fractions   Inch to mm Conversion   mm to Inch Conversion
  Decimal Equivalents of Letter Size Drills   Guide for Cutting Speeds & Feeds for Drills   Machinist Calculator

Hand Tappers

A hand tapping fixture allows precise, perpendicular, tap-to-hole alignment plus it reduces
 tap breakage that can easily occur when too much torque and/or side forces are applied.
The Phase2+ tapper is a superior product in terms of design, material & workmanship.
Hand tapper includes a set of adapters: #6, #8, #10, ¼", 5/16", ⅜", 7/16", ½" & ⅝".
The tap is first fixed to the adapter & then snapped into the spindle.
The handle has two different lengths to modulate the hand torque & it can be easily
removed as it is held in by a tapered pin. For small taps the knurled finger knob is used.
The adjustable counter-weight applies a slight upward force that aids unthreading the tap.
If the adapter is snapped in without a tap, it can be more easily removed by
first rotating the flat detent spring to release the ball bearing detent.
Be careful to not lose the ball detent.

Detail of the spring-loaded ball bearing detent for adapter retention in the precision ground spindle.
The flat spring has been rotated to expose the ball bearing detent. The vise is allowed to float in two
 directions enabling easy tap/hole alignment. The example shows tapping eight, #7 holes, with ¼-20
threads. A rotary table was used to drill every 45°.

To steady the hand tapper, 5/16-18 SS bolts screw into bench hard points.
The ¾" holes were drilled using a Forstner bit. The hard points are held in underneath by wood screws.
I remove the tapper when not in use & screw the bolts up from the bottom until they are flush.
The bolt-down hole has also been ⅜-16 threaded to use the clamping studs, as needed.

Always chamfer the hole first & use the proper thread-cutting fluid.
Caution: For soft materials (aluminum, brass, plastic) use a smaller hole for 75% threads & for harder
materials (steel, SS) use a larger tap hole for 50% threads to reduce tap breakage. See tap hole tables.
Certain materials, e.g., cast iron, can crumble, so coarse threads are easier to
cut more successfully than fine. Softer steels can have higher percentage threads (in the 60s).
There are formulae for calculating any desired percentage threads or use the Machinist Calculator.

The set of hand tapper adapters: The leftmost is a custom made, aluminum adapter for a ⅛-27 NPT tap.
Then left to right are ⅝", ½", ⅜" (2), 7/16", 5/16" (2), ¼", #10, #8, & #6 hardened steel tap adapters.




Each adapter has a round hole with a setscrew to hold the tap in &
a square hole at the end that positively engages the tap in order to prevent rotation.
Note the recess for the spring-loaded detent. A spiral-fluted bottoming tap is shown.

This is a small hand tapper with adapters for seven different tap sizes 0-80 through 5/16-18.
Each hex-shaped adapter has a square hole & a setscrew to securely engage & hold the tap shank.
The shaft rotates in a pressed-in, reamed brass bearing. The chromed stop pin can be removed to
provide more table room for the vise/part. The pin's hole can also be used to bolt-down to a bench hard point.
The finger knob is used with smaller taps to allow better feel & lower torque thus reducing chances of breakage.
The steel table is 8.5" x 6", the clearance height is 3.75", the throat depth is 4.5", & the overall height is 9".

This example shows a 0-80 tapping operation where a 3/64" tap hole is required for a 75% thread.

Tapping 6-32 threads into a brass weight.

Tapping 2-56 threads into the end of a brass rod.

Tap Handles

Differently sized tap handles correspond to various tap-size ranges.
Top: The two larger handles are Craftsman (USA).
Middle: The one medium-sized handle is from Germany.
Bottom: The two smaller Starrett (USA) handles have superior design & quality.

 

Large handle is being used to tap 75% ⅜-16 threads in aluminum.
The smaller blue vise holds the part for transfer to different machining setups.

Maximum chuck capacity is 0.502". This larger tap handle holds up to the 1-1/16" H hand reamer.

Cutting Fluids

Always use the appropriate cutting fluid. Some fluids are specific (e.g., for aluminum) while others generic.
Kerosene works very well for aluminum.


Micro-tap handles for very small (#0 to #6 & M1.6 to M3.5) sizes. Allows good feel while cutting threads.

Tap wrenches of various sizes.
The two black wrenches (left) have integral guides that mount in a drill press, mill, or lathe chucks.
The ratchet-type tap wrench (right of center) is useful in tight places. Tap wrenches usually have a
center-drilled hole on the end that can be used with a spring-loaded guide. Smaller taps, themselves,
have a chamfered (pointed) shank end & larger taps have a center-drilled hole to use with guides.

A large, chrome-plated ratchet-type (CW, lock, CCW) tap wrench with a capacity of ¼" ~ ½" (M6 ~ M14).
The two handles slide out for added leverage & slide in (or to one side) allowing use in tight places.

This tap handle holds up to the ¾" E hand reamer.

Tap handles with sturdy integral end guides (USA). Top left to right: ½" ~ ¾" & ¼" ~ ½". Bottom: 0 ~ ¼".

6-32 drilled & tapped (50% threads for steel) in the 9x20 lathe cross slide table back end.
This particular tap handle worked nicely as it has a guide that is mounted into the drill press chuck.
The large steel part is 9¾ inches long. Everything is securely clamped.

Drilling a 7/32" hole in the end of a 0.79" x 19.7" (20mm x 500mm) steel rod in preparation for a ¼-20 thread.
The long rod passes through the hole & hangs below the table surface of the large floor drill press.

Smaller tap wrench.
 

Larger tap wrench.
 

The lowest speed can usually keep the chuck from turning but sometimes I use a Tommy bar in the chuck.

This tap handle slides on a steel rod & the 1" diameter handle that does not easily over torque the tap.
The long, precision fitted guide rod gives excellent, rigid support & tapping range.

Wooden tap wrench holder.

 

A Yankee No. 251 (North Bros Mfg, Co., Philadelphia, PA, USA) ratcheting tap wrench that has a brass body.

Tap Guides

Shop fabricated steel (left) & aluminum (right) guides help start perpendicular tapping in difficult locations.
The series of holes match the US standard tap shank diameters. The smaller holes are for select drill bit sizes.
 

Clamping when possible helps.

Holes are threaded with a 6-32 tap for a Taig mill carriage modification.
This small Starrett tap handle has a smooth, ideal shape.

 

 

Steel tap guides for both standard & metric sizes (USA). Some smaller guide holes would be useful.

 

The bottom is precision ground & has a V-groove to allow accurate centering when tapping round parts.

 

Self-aligning tap & reamer fixture (China). Jaws needed deburring. Variable quality; not recommended.
Useful for making tapped holes outside of the controlled environment of the workshop.

 

 

Supplied with two sets (small & large) hardened jaws to accommodate a 0-80 to ½-13 tap size range.
The handle is too large for small taps & too small for large taps unless the material is soft, e.g., Delrin.

 

The base has two, 120° Vees for centering on round stock.

 

This tap guide (top) has a hardened, reversible tip. The pointed end fits into a center-drilled tap wrench
end or the cupped end captures/guides the pointed end of a tap shank. Both have adjustable spring tension
via the setscrew. A Taig spring-loaded center is shown (bottom) that also works well as a tap-wrench pivot.
Spring-loaded guide semi-automatically adjust out as the tap cuts deeper into the hole.

This photo shows how each tip type is used for the spring-loaded guide.

Tapmatic 30X

The Tapmatic 30X is expensive but can be found on the net for a good price, used.
It requires a torque bar attached to either the table or the quill. Fabrication details are shown, below.
Handy device if many holes need to be tapped using the mill. Tapmatic 30X instructions.

 

Milling a 3.6" hole on the rotary table.

Tapping an 8-32 thread on one side of the slot followed by drilling a clearance hole on the other side.

 

Milling a slot for the quill clamp.

 

The torque bar is a ⅜" steel rod fastened by a 10-32 bolt with a washer.

 

Die Holders

Die handles: Top one (India) is for 1½" diameter dies (a split-type is shown), next one is for hex-style dies.
The hex die-to-tap adapter is from the metric set. One-inch (GER) & 13/16" (USA) round-die holders shown.

Small dies & taps (left to right): 0-80, 1-72, M2-0.4 (in 13/16" die handle) 2-56, 3-48. Small red tap handle.

 

A handle that holds 20mm dies. An M6-1 left-hand die is shown.

 

Metric die & tap set (USA).

1" & 13/16" round die holder slides on a 9/16" steel rod with an MT2 adapter for the 9x20 lathe tailstock.
Refer to Machinery's Handbook for the proper major diameter dimensions for any given threaded rod.

The body is knurled for good grip & the removable steel bar can be added for more leverage.
Hand use without the bar gives good, low-torque control for threading delicate parts.


Die holders for threading while the part is on the lathe. The top holder is for 1.5" dies.

Drill-Tap Sets

Left to right: examples of tapered, plug & bottoming taps. ½-20 size shown.

Drill & taper tap sets (18 pieces each) left to right: metric, National Fine (NF) & National Coarse (NC).
Metric: M2.5-.45, M3-.5, M3.5-.6, M4-.7, M5-.8, M6-1, M8-1.25, M10-1.5, & M12-1.75.

NF:  6-40, 8-36, 10-24, 10-32, ¼-28, 5/16-24, ⅜-24, 7/16-20, & ½-20.

NC:  6-32, 8-32, 10-24, 10-32, ¼-20, 5/16-18, ⅜-16, 7/16-14, & ½-13.

Note: the drill bit sizes are for 75% threads in aluminum, brass & plastic.

 

 

Plug & bottom tap sets (USA). The spiral flutes are effective in removing swarf, especially from blind holes.

 

Spiral flutes effectively remove swarf.

HSS combination drill bit & tap. Imperial sizes: 4-40, 6-32, 8-32, 10-32, 10-24, ¼-28, ¼-20, 5/16-18, ⅜-16 & ½-13.

Combination drill bit, tap, & deburr/countersink. Metric sizes: M3x.5, M4x.7, M5x.8, M6x1, M8x1.25, & M10x1.5
Each HSS bit has an integral deburr/countersink & quick-change hex shaft.
Note the taper after the threading that prevents over drilling.

Imperial sizes: 6-32, 8-32, 10-24, 10-32, 12-24 & ¼-20. Variable quality in an import.

Unified Tap Drill Chart: Tap drill bit references for imperial, metric, & pipe threads.   Additional tap-drill charts.

Thread diameter.
 

Taper pipe thread tapping requires greater accuracy & it subjects the tools to higher stresses.
Pipe threads must be formed more accurately, because 100% of the thread height must be cut by
the tap or other pipe-threading tool to maintain the standard thread profile. A machinist looking at a
½-14 pipe tap is likely to note that the tap diameter is larger than ½". In fact, the tap's diameter at
the large end is 0.865". The tap's designation refers to the inner diameter (ID) of the standard iron
pipe it is designed to thread. Therefore, a ½-14 taper pipe thread tap is designed to tap a ½" ID
pipe. The external thread on a pipe with a ½" ID is at least the size of the ID plus the amount of
two wall thicknesses. To achieve the basic thread depth, drive the tap into the work piece 12 turns.

Trapezoidal (metric) screw thread has a 30° included angle. ACME screw thread has a 29° included angle.
Trapezoidal screw thread is made & measured in millimeters. ACME screw thread is made & measured in inches.
Trapezoidal screw thread pitch is stated in millimeters of pitch. ACME screw thread pitch is stated in threads per inch.

Formula for tap drill bit (round to closest available drill bit size): D1+(0.05 * p). Where: D1 = minimum internal thread minor diameter, p = pitch
 

Thread Measurement

Screw thread micrometer with five different anvil pairs to measure both unified &
metric external pitch diameter. 0" to 1" measurement range with a 0.0001" scale.

SCREW THREAD MICROMETER ANVILS
ANVIL #	1	2	3	4	5
TPI RANGE	64 - 48	44 - 28	24 - 14	13 - 9	8 - 5
METRIC RANGE	0.4 - 0.5	0.6 - 0.9	1 - 1.75	2 - 3	3.5 - 5

Anvil pairs are clearly marked for pitch range.

Example measurement of a ¼-20 screw. The micrometer reading is 0.2160". Table pitch value is 0.2164" max.
A fast & accurate thread measurement tool. The bolt can freely rotate around the micrometer's anvil axis.

Standard Unified & metric thread gages.

29° ACME (1n - 12n) & 30° ISO (2p - 20p) thread gages.

BOLT HEAD GRADE IDENTIFICATION MARKINGS - ASTM & SAE Standards
Grade Marking	Specification	Material	Bolt & Screw Size	Proof Load PSI	Tensile Strength MINIMUM PSI
	SAE - Grade 1	Low Carbon Steel	¼" - 1½"	33,000	60,000
	ASTM - A307	Low Carbon Steel	¼" - ½"   1½" - 4"	33,000	60,000  55,000
	SAE - Grade 2	Low Carbon Steel	¼" - ¾"  ¾" - 1½"	55,000  33,000	74,000  60,000
	SAE - Grade 3	Medium Carbon Steel Cold Worked	¼" - 1½"   ½" - ⅝"	85,000  80,000	110,000  100,000
	SAE - Grade 5 ASTM - A449	Medium Carbon Steel, Quenched & Tempered	¼" - 1" Over 1" - 1½"  Over 1½" - 3"	85,000 74,000  55,000	120,000 105,000   90,000
	ASTM - A325	Medium Carbon Steel, Quenched & Tempered	½", ⅝", ¾" ⅞", 1"  1⅛" - 1½"	85,000 78,000  74,000	120,000 115,000  105,000
	ASTM - A354 Grade BB	Low Alloy Steel, Quenched & Tempered	¼" - 2½"  Over 2½" - 4"	80,000  75,000	105,000  100,000
	ASTM - A354 Grade BC	Low Alloy Steel, Quenched & Tempered	¼" - 2½"  Over 2½" - 4"	105,000    95,000	125,000  115,000
	SAE - Grade 5.1	Low or Medium Carbon  Steel, Quenched & Tempered, with Assembled Lock Washer	Up to ⅜" incl.	85,000	120,000
	SAE - Grade 7	Medium Carbon Alloy Steel, Quenched & Tempered, Roll Threaded after Heat Treatment	¼" - 1½"	105,000	133,000
	SAE - Grade 8	Medium Carbon Alloy Steel,  Quenched & Tempered	¼" - 1½"	120,000	150,000
	ASTM - A354 Grade BD	Alloy Steel, Quenched & Tempered	¼" - 1½"	120,000	150,000
	ASTM - A490	Alloy Steel, Quenched & Tempered	½" - 2½"  Over 2½" - 4"	120,000  105,000	150,000  140,000

I buy metal hardware for 1USD per lb., at a local surplus store. It takes over 440 bins to keep it all sorted.

The newer polypropylene plastic drawers are much stronger & won't crack/break like the clear ones.

Hand Tappers, Tap Handles, Cutting Fluids, Tap Guides, Tapmatic 30X, Die Holders,
Drill-Tap Sets, Drill-Tap Chart, Thread Measurement, Bolt Head Grade Identification

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