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Tapping Threads & Associated Reference Tables

Hand Tappers, Tap Wrenches, Die Handles, Drill-Tap Sets, Drill-Tap Chart, Bolt Head Grade Identification

Refer to Introduction to Taps
 Single-point threading Section    How to Drill a Hole    Hand tapper manual.

 American National Unified Coarse & Fine Thread Dimensions with Tap Drill Sizes
American Standard Acme Screw Thread Dimensions
Double Depth of Screw Threads
ISO External Threads Tables

Decimal Equivalents of 8ths, 16ths, 32nds, 64ths
Decimal Equivalents of Number Size Drills
Decimal Equivalents of Letter Size Drills
Inch to Millimeter Conversion Table
Millimeter to Inch Conversion Table
Metric and Inch Equivalents Table
Temperature Conversion

Tap Drill Sizes for Fractional Size Threads Table
American Standard Pipe Thread & Tap Drill Sizes
Millimeter Tap Drill Sizes

Tapers & Angles Tables
Rules Relative to the Circle Tables
Guide for Cutting Speeds & Feeds for Drills
Tempering Colors
Triangle Chart

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" and 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 table, below.
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 % threads.

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




The adapter has a round hole with a set screw 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 set screw 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) a brass weight.

Tapping 2-56 in a brass rod.

Tap Wrenches

Differently sized tap wrenches.
The two larger (top) handles are Sears & the middle (sized) one is from Germany.
The two smaller (bottom) handles are LS Starrett & are of superior design & quality.

Micro-tap wrenches 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.
 

Large, ratchet-type (CW, lock, CCW) tap wrench. Capacity: ¼" ~ ½" (M6 ~ M14).
The two handles slide out for added leverage or slide in to allow use in tight places.

 

Make & use a tapping guide block to keep the tap perpendicular when hand tapping.
 

Steel & aluminum 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 sizes.

 

TAP SHANK GUIDE HOLE SIZES
Drill Size	W	P	G	#2	#8	#18	#28
Tap	⅜"	5/16"	¼"	#12	#10	#8	small

 

Small tap wrench.
 

Larger tap wrench.

 

The micro-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 set screw. A Taig spring-loaded center is shown (bottom) that also works well as a tap-wrench pivot.
A spring-loaded guide semi-automatically adjusts as the tap cuts deeper into the hole.

 

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.

 

Die Handles

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

 

Metric die & tap set (USA).

Examples of tapered, plug & bottoming taps.  ½-20 size shown.

 

Drill-Tap Sets

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 sizes are for 75% threads in aluminum, brass & plastic.

 

 

Plug & bottom tap sets (USA). The spiral flutes remove swarf from blind holes.

 

Spiral flutes effectively remove swarf.

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

Combination drill, 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.

SAE sizes: 6-32, 8-32, 10-24, 10-32, 12-24 & ¼-20.

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

Thread diameter.

Drilled holes are for clearance. The resulting hole size is often larger than the drill & may not be perfectly round.
 Precision holes are either reamed or bored.

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 ANVIL SIZES
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 0.2175".
A fast & accurate thread measurement tool. The bolt can freely rotate around the micrometer's anvil axis.

Standard Unified & metric 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

Hand Tappers, Tap Wrenches, Die Handles, Drill-Tap Sets, Drill-Tap Chart, Bolt Head Grade Identification