Category: Threaded Joints

Threaded joints are probably the most common form of mechanical assembly. They allow for the inexpensive but effective joining of parts.  This allows for less expensive manufacturing and easier maintenance, repair or servicing of a finished assembly.

To take advantage of threaded joints, you need to understand was standard sizes of threads exist, what types of bolts and hardware exist and what are the implications of different grades of hardware – in terms of size, mechanical properties, corrosion resistance and fastening strength.

Unified Screw Threads – Fine (UNF)

Unified Screw Threads – Course (UNC)

National Pipe Thread (NPT)

Metric Thread

ACME Thread

Socket Head Cap Screw (SHCS)

Hex Head Cap Screw (HHCS)

Button Head Cap Screw (BHCS)

Posted on

Metric Hex Bolt Head Size

Do you ever struggle to remember the relationship between a metric hex bolt thread size and the related hex head size (between the flats, or ‘wrench’ size).

Or, do you have a design with limited clearance?  Use this table to see if you have room, but don’t forget to check that you have enough room for a socket or a wrench to get in there.  Otherwise, you might be better off using a Socket Head Cap Screw (SHCS) instead of a Hex Head fastener.

The first column (ANSI/ISO) is pertinent to ‘standard’ metric  hex bolts:

Bolt Diameter
(mm)		 Head/Wrench Size
(mm)
ANSI/ISO DIN JIS DIN/ISO
Heavy Hex
4 7 7 7 –
5 8 8 8 –
6 10 10 10 –
7 – 11 – –
8 13 13 12 –
10 16 17 14 –
12 18 19 17 22/21*
14 21 22 19 –
16 24 24 22 27
18 – 27 – –
20 30 30 – 34/32*
ANSI – American National Standards Institute
ISO – International Organization for Standardisation
DIN – Deutsches Institut fur Normung
JIS – Japanese Industrial Standard
* Indicates ISO standard.

Learn more about threaded joints.

 

Posted on

National Pipe Thread (NPT) Tap Drill Size

Below is the National Pipe Thread – NPT Tap Drill Size Chart.  It tells us what size hole must be drilled to begin tapping the tapered NPT thread.

Standard NPT Tap Drill Sizes
NPT Size
 Tap Drill Size (in.)
Decimal Equivalent (in.)
1/16 – 27
“C”
0.242
1/8 – 27
“Q”
0.332
1/4 – 18
7/16
0.438
3/8 – 18
9/16
0.562
1/2 – 14
45/64
0.703
3/4 – 14
29/32
0.906
1.0 – 11•1/2
1•9/64
1.141
1•1/4 – 11•1/2
1•31/64
1.484
1•1/2 – 11•1/2
1•23/32
1.719
2.0 – 11•1/2
2•3/16
2.188
2•1/2 – 8
2•39/64
2.609
3.0 – 8
3•15/64
3.234

Metric Tap Drill Sizes
Standard UNC Tap Drill Sizes
Standard UNF Tap Drill Sizes

Posted on

National Pipe Thread (NPT) Sizes / Dimensions

What is the outer diameter of a pipe thread?  Pipes are odd in that their size is based roughly on the inner diameter of the pipe.  So when you have a National Pipe Thead – NPT fitting, the thread size is actually much larger than the name implies.


Pipe thread sizes

Nominal
NPT Size		 Outer
Diameter
inch (mm)		 Threads
per inch		 Pitch
of Thread
inch (mm)
1/16“ 0.3125 in (7.94 mm) 27 0.03704 in (0.94082 mm)
⅛” 0.405 in (10.29 mm) 27 0.03704 in (0.94082 mm)
¼” 0.540 in (13.72 mm) 18 0.05556 in (1.41122 mm)
3/8″ 0.675 in (17.15 mm) 18 0.05556 in (1.41122 mm)
½” 0.840 in (21.34 mm) 14 0.07143 in (1.81432 mm)
¾” 1.050 in (26.67 mm) 14 0.07143 in (1.81432 mm)
1″ 1.315 in (33.40 mm) 11½ 0.08696 in (2.20878 mm)
1¼” 1.660 in (42.16 mm) 11½ 0.08696 in (2.20878 mm)
1½” 1.900 in (48.26 mm) 11½ 0.08696 in (2.20878 mm)
2″ 2.375 in (60.33 mm) 11½ 0.08696 in (2.20878 mm)
2½” 2.875 in (73.02 mm) 8 0.12500 in (3.175 mm)
3″ 3.500 in (88.90 mm) 8 0.12500 in (3.175 mm)
4″ 4.500 in (114.30 mm) 8 0.12500 in (3.175 mm)
5″ 5.563 in (141.30 mm) 8 0.12500 in (3.175 mm)
6″ 6.625 in (168.27 mm) 8 0.12500 in (3.175 mm)
10″ 10.750 in (273.05 mm) 8 0.12500 in (3.175 mm)
12″ 12.750 in (323.85 mm) 8 0.12500 in (3.175 mm)
14″ OD 14 in (355.60 mm) 8 0.12500 in (3.175 mm)
16″ OD 16 in (406.40 mm) 8 0.12500 in (3.175 mm)
18″ OD 18 in (457.20 mm) 8 0.12500 in (3.175 mm)
20″ OD 20 in (508.00 mm) 8 0.12500 in (3.175 mm)
24″ OD 24 in (609.60 mm) 8 0.12500 in (3.175 mm)
Definition of pipe thread acronyms
NPT National Pipe Thread
FPT Female Pipe Thread
MPT Male Pipe Thread
PTF SAE short taper pipe thread – dryseal
NPTF American National taper pipe thread for dryseal pressure-tight joints
NPSM American National straight pipe thread for mechanical joints
NPSI American National straight intermediate pipe thread
GHT Garden Hose Thread
NST Fire Hose Thread
BSPT British Standard taper pipe thread (metric dimensions)
Posted on

Hex Nut Grade Identification and Mechanical Properties

How strong are these nuts?  That’s what she said.  Seriously, what do those marks mean?  Should I order a hex nut with one dot or three dashes?  Here’s a cheat sheet with nut identifying marks, material grade and mechanical properties.


Grade
Identification
Marking		 Specification Material Nominal Size
In.		 Proof
Load
Stress
ksi		 Hardness
Rockwell		 See
Note
Min Max

No Mark		 ASTM A563 – Grade 0 Carbon Steel 1/4 thru 1-1/2 69 B55 C32 3,4
ASTM A563 – Grade A Carbon Steel 1/4 thru 1-1/2 90 B68 C32 3,4
ASTM A563 – Grade B Carbon Steel 1/4 thru 1 120 B69 C32 3,4
over 1 thru 1-1/2 105
ASTM A563 – Grade C Carbon Steel
May be Quenched
and Tampered		 1/4 thru 4 144 B78 C38 5
ASTM A563 – Grade C3 Atmospheric
Corrosion
Resistant Steel
May be Quenched
and Tampered		 1/4 thru 4 144 B78 C38 5,9
ASTM A563 – Grade D Carbon Steel
May be Quenched
and Tampered		 1/4 thru 4 150 B84 C38 6
ASTM A563 – Grade DH Carbon Steel
Quenched
and Tampered		 1/4 thru 4 175 C24 C38 6
ASTM A563 – Grade DH3 Atmospheric
Corrosion
Resistant Steel,
Quenched
and Tampered		 1/4 thru 4 175 C24 C38 5,9
ASTM A194 – Grade 1 Carbon Steel 1/4 thru 4 130 B70 — 7
ASTM A194 – Grade 2 Medium Carbon
Steel		 1/4 thru 4 150 159 352 7,8
ASTM A194 – Grade 2H Medium Carbon
Steel, Quenched
and Tempered		 1/4 thru 4 175 C24 C38 7
ASTM A194 – Grade 2HM Medium Carbon
Steel, Quenched
and Tempered		 1/4 thru 4 150 159 237 7,8
ASTM A194 – Grade 4 Medium Carbon
Alloy Steel,
Quenched
and Tempered		 1/4 thru 4 175 C24 C38 7
ASTM A194 – Grade 7 Medium Carbon
Alloy Steel,
Quenched
and Tempered		 1/4 thru 4 175 C24 C38 7
ASTM A194 – Grade 7M Medium Carbon
Alloy Steel,
Quenched
and Tempered		 1/4 thru 4 150 159 237 7
See Note 1,2 10
Posted on

Hex Bolt Identifying Marks, Material Grade and Mechanical Properties

Are you confused about the modest hex bolt, or are you wondering what all those marks mean?  This table will help you identify any hex bolt right on the nuts, and it will also tell you about the material grade and mechanical properties.  What more could you ask for from a super boring table?

Hex Bolt Identification
Grade Mark		 Specification Fastener
Description		 Material Nominal Size
Range (in.)		 Mechanical Properties
Proof Load
(psi)		 Yield Strength
Min (psi)		 Tensile Strength
Min (psi)

No
Grade
Mark		 SAE J429
Grade 1		 Bolts,
Screws,
Studs		 Low or Medium Carbon Steel 1/4 thru 1-1/2 33,000 36,000 60,000
ASTM A307
Grades A&B		 Low Carbon Steel 1/4 thru 4 — —
SAE J429
Grade 2		 Low or Medium Carbon Steel 1/4 thru 3/4 Over 3/4 to 1-1/2 55,000
33,000		 57,000
36,000		 74,000
60,000

No
Grade
Mark		 SAE J429
Grade 4		 Studs Medium Carbon Cold Drawn Steel 1/4 thru 1-1/2 — 100,000 115,000

B5		 ASTM A193
Grade B5		 AISI 501 1/4 Thru 4 — 80,000 100,000

B6		 ASTM A193
Grade B6		 AISI 410 85,000 110,000

B7		 ASTM A193
Grade B7		 AISI 4140, 4142, OR 4105 1/4 thru 2-1/2
Over 2-1/2 thru 4
Over 4 thru 7		 —
—
—		 105,000
95,000
75,000		 125,000
115,000
100,000

B16		 ASTM A193
Grade B16		 CrMoVa Alloy Steel 105,000
95,000
85,000		 125,000
115,000
100,000

B8		 ASTM A193
Grade B8		 AISI 304 1/4 and larger — 30,000 75,000

B8C		 ASTM A193
Grade B8C		 AISI 347

B8M		 ASTM A193
Grade B8M		 AISI 316

B8T		 ASTM A193
Grade B8T		 Bolts,
Screws,
Studs for High-Temperature Service		 AISI 321 1/4 and larger — 30,000 75,000

B8		 ASTM A193
Grade B8		 AISI 304
Strain Hardened		 1/4 thr 3/4
Over 3/4 thru 1
Over 1 thru 1-1/4
Over 1-1/4 thru 1-1/2		 —
—
—
—		 100,000
80,000
65,000
50,000		 125,000
115,000
105,000
100,000

B8C		 ASTM A193
Grade B8C		 AISI 347
Strain Hardened

B8M		 ASTM A193
Grade B8M		 AISI 316
Strain Hardened		 95,000
80,000
65,000
50,000		 110,000
100,000
95,000
90,000

B8T		 ASTM A193
Grade B8T		 AISI 321
Strain Hardened		 100,000
80,000
65,000
50,000		 125,000
115,000
105,000
100,000

L7		 ASTM A320
Grade L7		 Bolts,
Screws,
Studs for Low-Temperature Service		 AISI 4140,
4142 or 4145		 1/4 thru 2-1/2 — 105,000 125,000

L7A		 ASTM A320
Grade L7A		 AISI 4037

L7B		 ASTM A320
Grade L7B		 AISI 4137

L7C		 ASTM A320
Grade LC7		 AISI 8740

L43		 ASTM A320
Grade L43		 AISI 4340 1/4 thru 4 — 105,000 125,000

B8		 ASTM A320
Grade B8		 Bolts,
Screws,
Studs for Low-Temperature Service		 AISI 304 1/4 and larger — 30,000 75,000

B8C		 ASTM A320
Grade B8C		 AISI 347

B8T		 ASTM A320
Grade B8T		 AISI 321

B8F		 ASTM A320
Grade B8F		 AISI 303
or 303Se

B8M		 ASTM A320
Grade B8M		 AISI 316

B8		 ASTM A320
Grade B8		 AISI 304 1/4 thru 3/4
Over 3/4 thru 1
Over 1 thru 1-1/4
Over 1-1/4 thru 1-1/2		 —
—
—
—		 100,000
80,000
65,00
50,00		 100,000
80,000
65,00
50,00

B8C		 ASTM A320
Grade B8C		 AISI 347

B8F		 ASTM A320
Grade B8F		 AISI 303
or 303Se

B8M		 ASTM A320
Grade B8M		 AISI 316

B8T		 ASTM A320
Grade B8T		 AISI 321
SAE J429
Grade 5		 Bolts,
Screws,
Studs		 Medium Carbon Steel, Quenched and Tempered 1/4 thru 1
Over 1 to 1-1/2		 85,000
74,000		 92,000
81,000		 120,000
105,000
ASTM A449 1/4 thru 1
Over 1 to 1-1/2
Over 1-1/2 thru 3		 85,000
74,000
55,000		 92,000
81,000
58,000		 120,000
105,000
90,000
SAE J429
Grade 5.1		 Sems Low or Medium Carbon Steel, Quenched and Tempered No. 6
thru 3/8		 85,000 — 120,000
SAE J429
Grade 5.2		 Bolts,
Screws,
Studs		 Low Carbon Martensitic Steel, Quenched and Tempered 1/4 thru 1 85,000 92,000 120,000

A325		 ASTM A325
Type 1		 High Strength
Structural Bolts		 Medium Carbon Steel, Quenched and Tempered 1/2 thru 1
1-1/8 thru 1-1/2		 85,000
74,000		 92,000
81,000		 120,000
105,000

A325		 ASTM A325
Type 2		 Low Carbon Martensitic Steel, Quenched and Tempered 1/2 thru 1 85,000 92,000 120,000

A325		 ASTM A325
Type 3		 Atmospheric Corrosion Resisting Steel, Quenched and Tempered 1/2 thru 1
1-1/8 thru 1-1/2		 85,000
74,000		 92,000
81,000		 120,000
105,000

BB		 ASTM A354
Grade BB		 Bolts,
Studs		 Alloy Steel, Quenched and Tempered 1/4 thru 2-1/2
2-3/4 thru 4		 80,000
75,000		 83,000
78,000		 105,000
100,000

BC		 ASTM A354
Grade BC		 105,000
95,000		 109,000
99,000		 125,000
115,000
SAE J429
Grade 7		 Bolts,
Screws,		 Medium Carbon Alloy Steel, Quenched and Tempered 4 1/4 thru 1-1/2 105,000 115,000 133,000
SAE J429
Grade 8		 Bolts,
Screws,
Studs		 Medium Carbon Alloy Steel, Quenched and Tempered 1/4 thru 1-1/2 120,000 130,000 150,000
ASTM A354
Grade BD		 Alloy Steel, Quenched and Tempered 4

No Grade
Mark		 SAE J429
Grade 8.1		 Studs Medium Carbon Alloy or SAE 1041 Modified Elevated Temperature Drawn Steel 1/4 thru 1-1/2 120,000 130,000 150,000

A490		 ASTM A490 High Strength Structural Bolts Alloy Steel, Quenched and Tempered 1/2 thru 1-1/2 120,000 130,000 150,000 min
170,000 max

No Grade
Mark		 ISO R898
Class 4.6		 Bolts,
Screws,
Studs		 Medium Carbon Steel, Quenched and Tempered All Sizes
thru 1-1/2		 33,000 36,000 60,000

No Grade
Mark		 ISO R898
Class 5.8		 55,000 57,000 74,000
8.8

or

88		 ISO R898
Class 8.8		 Alloy Steel, Quenched and Tempered 85,000 92,000 120,000
10.9

or

109		 ISO R898
Class 10.9		 120,000 130,000 150,000

Your hex bolt may require a hex nut.

Posted on

Flat Washer Dimensions (ASME B18.22.1)

How much space do you need for a bolt if you are using a flat washer?  How long do your threads need to be if you are accounting for the thickness of a washer.  Flat washer dimensions are frequently important while working on mechanical designs.  While there are many size options available, here is a table for the most common flat washer dimensions.


Bolt Size A B C Weight In Pounds
Per 100 Pieces
Inside Diameter Outside Diameter Thickness
3/8 7/16 1 0.083 2
1/2 9/16 1-3/8 0.109 4
5/8 11/16 1-3/4 0.134 8
3/4 13/16 2 0.148 11
7/8 15/16 2-1/4 0.165 15
1 1-1/16 2-1/2 0.165 19
1-1/8 1-1/4 2-3/4 0.165 22
1-1/4 1-3/8 3 0.165 26
1-3/8 1-1/2 3-1/4 0.180 33
1-1/2 1-5/8 3-1/2 0.180 38
1-5/8 1-3/4 3-3/4 0.180 43
1-3/4 1-7/8 4 0.180 50
1-7/8 2 4-1/4 0.180 57
2 2-1/8 4-1/2 0.180 63
2-1/4 2-3/8 4-3/4 0.220 83
2-1/2 2-5/8 5 0.238 96
2-3/4 2-7/8 5-1/4 0.259 110
3 3-1/8 5-1/2 0.284 130
Posted on

Hex Nut Dimensions

There are lots of reasons you need to know hex nut dimensions.  You need to hex nut height to determine the best length of a fastener in a bolted assembly.  You need to know the size of the hex to make sure you have sufficient clearance for the nut itself, the washer and a wrench.


Size Across Flats* Height
Hex Nut Machine Screw Nut Hex Nut Jam Nut Nylock Nut Machine Screw Nut
0 – 5/32 – – – 3/64
1 – 5/32 – – – 3/64
2 – 3/16 – – 9/64 1/16
3 – 3/16 – – 9/64 1/16
4 – 1/4 – – 9/64 3/32
6 – 5/16 – – 11/64 7/64
8 – 11/32 – – 15/64 1/8
10 – 3/8 – – 15/64 1/8
12 – 7/16 – – 5/16 5/32
1/4 7/16 7/16 7/32 5/32 5/16 3/16
5/16 1/2 9/16 17/64 3/16 11/32 7/32
3/8 9/16 5/8 21/64 7/32 29/64 1/4
7/16 11/16 – 3/8 1/4 29/64 –
1/2 3/4 – 7/16 5/16 19/32 –
9/16 7/8 – 31/64 5/16 41/64 –
5/8 15/16 – 35/64 3/8 3/4 –
3/4 1-1/8 – 41/64 27/64 7/8 –
7/8 1-5/16 – 3/4 31/64 63/64 –
1 1-1/2 – 55/64 35/64 1-3/64 –
* This is also the size of wrench to use.
Posted on

Hex Cap Bolt Dimensions

Hex cap bolt dimensions are trickier than you think.  By default, they are not threaded all the way, so you need to be careful in your design to make sure you are not threading beyond the capability of the bolt itself.

Just as with the standard nut and washer, it it important to consider the geometric constraints of the hex cap bolt to ensure proper function and easier assembly / disassembly.


Hex Bolt Dimensions s
Basic Product Diameter
Full-Size Body Diameter
Width Across Flats
Width Across Corners
Head Height
Thread Length
Thread Length
Max
Min
Max
Min
Up to 6in
Over 6 in
1/4
.26
.237
7/16
.505
0.484
11/64
0.75
1.00
5/16
.324
.298
1/2
.577
0.552
7/32
0.88
1.13
3/8
.388
.360
9/16
.650
0.62
1/4
1.00
1.25
7/16
.452
.421
5/8
.722
0.687
19/64
1.13
1.38
1/2
.515
.482
3/4
.866
0.826
11/32
1.25
1.50
5/8
.642
.605
15/16
1.083
1.033
27/64
1.50
1.75
3/4
.768
.729
1-1/8
1.299
1.24
1/2
1.75
2.00
7/8
.895
.852
1-5/16
1.516
1.447
37/64
2.00
2.25
1
1.022
.976
1-1/2
1.732
1.653
43/64
2.25
2.50
1-1/8
1.149
1.098
1-11/16
1.949
1.859
3/4
2.50
2.75
1-1/4
1.277
1.223
1-7/8
2.165
2.066
27/32
2.75
3.00
1-3/8
1.404
1.345
2-1/16
2.382
2.273
29/32
3.00
3.25
1-1/2
1.531
1.47
2-1/4
2.598
2.48
1
3.25
3.50
1-3/4
1.785
1.716
2-5/8
3.031
2.893
1-5/32
3.75
4.00
2
2.039
1.964
3
3.464
3.306
1-11/32
4.25
4.50
2-1/4
2.305
2.214
3-3/8
3.897
3.719
1-1/2
4.75
5.00
2-1/2
2.559
2.461
3-3/4
4.33
4.133
1-21/32
5.25
5.5
2-3/4
2.827
2.711
4-1/8
4.763
4.546
1-13/16
5.75
6.00
3
3.081
2.961
4-1/2
5.196
4.959
2
6.25
6.50
3-1/4
3.335
3.21
4-7/8
5.629
5.372
2-3/16
6.75
7.00
3-1/2
3.589
3.461
5-1/4
6.062
5.786
2-5/16
7.25
7.50
3-3/4
3.858
3.726
5-5/8
6.495
6.198
2-1/2
7.75
8.00
4
4.111
3.975
6
6.928
6.612
2-11/16
8.25
8.50

 

Posted on

Metric Thread – Tap Drill / Clearance Drill

Below is a table for metric tap drill sizes.  It covers both threaded holes (when you are cutting thread) and clearance holes (when you are simply placing a bolt through a hole).


Metric Tap Drill Chart
Tap size Major
Dia (mm)		 Threads
per 		Tap Drill
(mm)		 Tap Drill
(inch)		 Clearance Hole
(mm)		 Clearance Hole
(inch)
M1.6×0.35 1.6 0.35 1.25 #55 1.8 #49
M2x0.4 2.0 0.40 1.60 #52 2.4 #41
M2.5×0.45 2.5 0.45 2.05 #46 2.9 #32
M3x.05 3.0 0.50 2.50 #39 3.4 #29
M3.5×0.6 3.5 0.60 2.90 #32 3.9 #23
M4x0.7 4.0 0.70 3.30 #30 4.5 #16
M5x0.8 5.0 0.80 4.20 #19 5.5 7/32
M6x1 6.0 1.00 5.0 #8 6.6 G
M8x1.25 8.0 1.25 6.8 H 9.0 T
M8x1 8.0 1.00 7.0 J 9.0 T
M10x1.5 10.0 1.50 8.5> R 12.0 31/64
M10x1.25 10.0 1.25 8.8 11/32 12.0 31/64
M12x1.75 12.0 1.75 10.2 13/32 14.0 35/64
M12x1.25 12.0 1.25 10.8 27/64 14.0 35/64
M14x2 14.0 2.00 12.0 15/32 16.0 5/8
M14x1.5 14.0 1.5 12.5 1/2 16.0 5/8
M16x2 16.0 2.00 14.0 35/64 18.0 45/64
M16x1.5 16.0 1.50 14.5 37/64 18.0 45/64
M18x2.5 18.0 2.50 15.5 39/64 20.0 51/64
M18x1.5 18.0 1.50 16.5 21/32 20.0 51/64
M20x2.5 20.0 2.50 17.5 11/16 22.0 7/8
M20x1.5 20.0 1.50 18.5 47/64 22.0 7/8
M22x2.5 22.0 2.50 19.5 49/64 25.0 1
M22x1.5 22.0 1.50 20.5 13/16 25.0 1
M24x3 24.0 3.00 21.0 53/64 27.0 1-5/64
M24x2 24.0 2.00 22.0 7/8 27.0 1-5/64
M27x3 27.0 3.00 24.0 15/16 30.0 1-3/16
M27x2 27.0 2.0 25.0 1 30.0 1-3/16

Standard UNC Tap Drill Sizes
Standard UNF Tap Drill Sizes
Standard NPT Tap Drill Sizes

Posted on

Tap Drill Size – UNF

Below is a table of drill and tap sizes for Unified Screw Threads – Fine, UNF.

UNF screws may not always be appropriate.  Depending on the application, you may be better off using UNC fasteners.


INCH SIZES – NATIONAL FINE
TAP SIZE DRILL SIZE
#1-72 #53
#2-64 #50
#3-56 #46
#4-48 #42
#5-44 #37
#6-40 #33
#8-36 #29
#10-32 #21
#12-28 #15
1/4-28 #3
5/16-24 I
3/8-24 Q
7/16-20 W
1/2-20 29/64
9/16-18 33/64
5/8-18 37/64
3/4-16 11/16
7/8-14 13/16
1″-12 15/16
1-1/8-12 1-3/64
1-1/4-12 1-11/64
1-1/2-12 1-27/64
1-3/4-12 1-43/64
2″-12 1-59/64

Metric Tap Drill Sizes
Standard UNC Tap Drill Sizes
Standard NPT Tap Drill Sizes