Carriage Bolts: Dimensions & Specifications

Carriage Bolts: Round Head Square Neck

Carriage Bolts - Round Head, Square Neck Drawing

Carriage Bolts: Round Head, Square Neck (ASME B18.5-1990)

Basic Bolt Diameter

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Body Diameter (E)

Head Diameter (A) Head Height (H) Square Width (O) Square Depth (P)
Max Min  Max  Min  Max Min  Max Min Max Min
8 .1640 .157 .328 .298 .102 .083 .169 .155 .108 .078
10 .1900 .182 .436 .436 .114 .094 .199 .185 .125 .094
12 .2160 .206 .500 .468 .149 .125 .215 .197 .135 .105
1/4 .2500 .237 .594 .563 .145 .125 .260 .245 .156 .125
5/16 .3125 .298 .719 .688 .176 .156 .324 .307 .187 .156
3/8 .3750 .360 .844 .782 .208 .188 .388 .368 .219 .188
7/16 .4375 .421 .969 .907 .239 .219 .452 .431 .250 .219
1/2 .5000 .483 1.094 1.032 .270 .250 .515 .492 .281 .250
5/8 .6250 .605 1.344 1.219 .344 .313 .642 .616 .344 .313
3/4 .7500 .729 1.594 1.469 .406 .375 .768 .741 .406 .375

 

Carriage Bolts: Round Head, Square Neck: Tolerance on Length
Nominal Bolt Size
Nominal Bolt Length
Up to 1" Over 1" - 2-1/2" Over 2-1/2" - 4"  Over 4" - 6" Longer than 6"
No. 8 - 3/8 +.02, -.03 +.02, -.04 +.04, -.06 +.06, -.10 +.10, -.18
7/16 & 1/2  +.02, -.03 +.04, -.05 +.06, -.08 +.08, -.10 +.12, -.18
9/16 - 3/4  +.02, -.03 +.06, -.08 +.08, -.10 +.10, -.10 +.14, -.18

 

- Length of a carriage bolt is measured from the underhead bearing surface to the extreme end of the bolt.

- ASME B18.5-1990 does not specify dimensions for the #8 or #12 diameters. Data listed for these sizes is independent of the ASME specification.

Low Carbon & Hot Dipped Galvanized Carriage Bolt
 

Low Carbon Steel

Carriage Bolt Low Carbon Bolt Head Marking

Hot Dipped Galvanized Steel

Carriage Bolt Low Carbon Hot Dip Galvanized Bolt Head Marking

Description Round head bolt with square neck and a unified thread pitch. Made from low or medium carbon steel. Round head bolt with square neck and a unified thread pitch. Made from low or medium carbon steel with a galvanized zinc finish.
Applications The square neck is designed to keep the bolt from turning as the nut is tightened. Often used for outdoor furniture because of the thicker protective coating.
Material
AISI 1006-1050 or equivalent steel AISI 1006-1050 or equivalent steel
Core Hardness Rockwell B70-B100 Rockwell B70-B100
Proof Load 33,000 psi  
Yield Strength 36,000 psi min.  
Tensile Strength 60,000 psi min.  
Elongation 18% min  
Reduction of Area 35% min  
Minimal Thread Length The minimum length of thread shall be equal to twice the basic bolt diameter plus .025" for bolts <6", and twice the diameter plus .50" for bolts >6".
Grades-5 & 8 Carriage Bolts
 

Grade-5

Grade 5 Carriage Bolt Head Marking

Grade-8

 Grade 8 Carriage Bolt Head Marking

Description Carriage bolt made from medium carbon steel and heat-treated Carriage bolt made from medium carbon alloy steel and heat-treated.
Applications Greater load carrying capacity compared to a low carbon carriage bolt. Greater load carrying capacity compared to a Grade-5 carriage bolt.
Material
AISI 1030-1050 or equivalent steel Medium carbon alloy steel
Heat Treatment Heat treated, oil or water-quenched, and tempered at min. 800 Degrees (F) Heat treated, oil-quenched, and tempered at min. 800 Degrees (F)
Core Hardness 1/4 - 1" Diameter: Rockwell C25-C34 1/4 - 1" Diameter: Rockwell C33-C39
Surface Hardness 1/4 - 1" Diameter: Rockwell 30N54 max 1/4 - 1" Diameter: Rockwell 30N 58.6 max
Proof Load 1/4 - 1" Diameter: 85,000 psi 1/4 - 1" Diameter: 120,000 psi
Yield Strength 1/4 - 1" Diameter: 92,000 psi min 1/4 - 1" Diameter: 130,000 psi min
Tensile Strength 1/4 - 1" Diameter: 120,000 psi 1/4 - 1" Diameter: 150,000 psi min
Elongation 14% Min 12% Min
Reduction of Area 35% Min 35% Min
Minimal Thread Length The minimum length of thread shall be equal to twice the basic bolt diameter plus .025" for bolts <6", and twice the diameter plus .50" for bolts >6".
Plating   Typically Zinc Yellow
Stainless Steel 18-8 Carriage Bolt
 

Stainless Steel 18-8

Stainless Steel Carriage Bolt Head Marking

Description Round head bolt with a square neck under the head, unified thread pitch, made from austenitic alloy stainless steel.
Applications Use in environments which require general atmospheric corrosion resistance.
Material
Made from any of the following: 302, HQ, 303, 303Se, 304, XM7 (Chromium Content 17-19% and Nickel Content 8-10%)
Heat Treatment The austenitic alloys develop their strength through work hardening during the fastener manufacturing process. The only heat treatment normally available on austenitic stainless alloys is annealing, which is done at approx. 1900 Degrees (F) to a dead soft condition and is not normally thermally reversible.
Hardness 1/4 - 1/2" Diameter: Rockwell B95-C32
Yield Strength 1/4" - 1/2", 2.25 Diameter and Longer: 65,000 psi min
Tensile Strength 1/4 - 1/2" Diameter, 2.25 Diameter and longer: 100,000-150,000 psi min
Elongation in 4D 1/4" - 1/2" Diameter: 20% min
Minimal Thread Length The minimum length of thread shall be equal to twice the basic bolt diameter plus .025" for bolts <6".

 

  

Carriage Bolts: Round Head Short Neck


Carriage Bolt Round Head, Short Neck Drawing at AFT Fasteners

Carriage Bolts: Round Head, Short Neck (ANSI/ASME B18.5)

Nominal Size or Basic Bolt Diameter

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Body Diameter (B)

Head Diameter (W) Head Height (H) Square Width (S) Square Depth (N) Corner Radius on Square (C) Fillet Radius (R)
Max Min  Max  Min  Max Min  Max Min Max Min Max Max
1/4 .2500 .260 .213 .594 .563 .145 .125 .260 .245 .124 .093 .031 .031
5/16 .3125 .324 .272 .719 .688 .176 .156 .324 .307 .124 .093 .031 .031
3/8 .3750 .388 .329 .844 .782 .208 .188 .388 .368 .156 .125 .047 .031
7/16 .4375 .452 .385 .969 .907 .239 .219 .452 .431 .156 .125 .047 .031
1/2 .5000 .515 .444 1.094 1.032 .270 .250 .515 .492 .156 .125 .047 .031
5/8 .6250 .642 .559 1.344 1.219 .344 .313 .642 .616 .218 .187 .078 .062
3/4 .7500 .768 .678 1.594 1.469 .406 .375 .768 .741 .218 .187 .078 .062

 

Carriage Bolts: Round Head, Short Neck: Tolerance on Length
Nominal Bolt Size
Nominal Bolt Length
Up to 1" Over 1" - 2-1/2" Over 2-1/2" - 4"  Over 4" - 6" Longer than 6"
No. 10 - 3/8 +.02, -.03 +.02, -.04 +.04, -.06 +.06, -.10 +.10, -.18
7/16 & 1/2  +.02, -.03 +.04, -.05 +.06, -.08 +.08, -.10 +.12, -.18
9/16 - 3/4  +.02, -.03 +.06, -.08 +.08, -.10 +.10, -.10 +.14, -.18
7/8 & 1   +.08, -.10 +.10, -.14 +.12, -.16 +.16, -.20
1-1/8 - 1-1/2   +.12, -.12 +.16, -.16 +.18, -.18 +.22, -.22

 

- Length of a carriage bolt is measured from the underhead bearing surface to the extreme end of the bolt.

Carriage Bolt: Round Head, Short Neck Properties
Description A round head bolt with a short, square shoulder under the head, and a unified thread pitch. The bolt is made from low or medium carbon steel
Applications Designed to keep the bolt from turning when a nut is being tightened. The short neck is used with sheet metal where a standard size neck would create an obstruction.
Material
AISI 1006-1050 or equivalent steel
Hardness Rockwell B70-B100
Proof Load 33,000 psi
Tensile Strength 60,000 psi min.
Yield Strength 36,000 psi min.
Elongation 18% min
Reduction of Area 35% min
Minimal Thread Length The minimum length of thread shall be equal to twice the basic bolt diameter plus .025" for bolts <6", and twice the diameter plus .50" for bolts >6".

 

 Carriage Bolts: Round Head, Ribbed Neck


Carriage Bolt Round Head, Ribbed Neck Drawing

Carriage Bolts: Round Head, Ribbed Neck (ASME B18.5-1998)

Nominal Size or Basic Bolt Diameter

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Body Diameter (B)

Head Diameter (W) Head Height (H) Head to Ribs (M) Number of Ribs Diameter Over Ribs (V) Depth Over Ribs (D) Fillet Radius (R)
Max Min  Max  Min  Max Min  Up to 7/8" Length 1"+ Length Approx. Min Up to 7/8" Length 1" & 1-1/8" Length 1-1/4"+ Length Max
No 10 .1900 .199 .182 .469 .438 .114 .094 .031 .063 9 .210 .250 .407 .594 .031
1/4 .2500 .260 .237 .594 .563 .145 .125 .031 .063 10 .274 .250 .407 .594 .031
5/16 .3125 .324 .298 .719 .688 .176 .156 .031 .063 12 .340 .250 .407 .594 .031
3/8 .3750 .388 .360 .844 .782 .208 .188 .031 .063 12 .405 .250 .407 .594 .031
7/16 .4375 .425 .421 .969 .907 .239 .219 .031 .063 14 .470 .250 .407 .594 .031
1/2 .5000 .515 .483 1.094 1.032 .270 .250 .031 .063 16 .534 .250 .407 .594 .031
5/8 .6250 .642 .605 1.344 1.219 .344 .313 .094 .094 19 .660 .313 .438 .625 .062
3/4 .7500 .768 .729 1.594 1.469 .406 .375 .094 .094 22 .785 .313 .438 .625 .062

 

Carriage Bolts: Round Head, Ribbed Neck: Tolerance on Length
Nominal Bolt Size
Nominal Bolt Length
Up to 1" Over 1" - 2-1/2" Over 2-1/2" - 4"  Over 4" - 6" Longer than 6"
No. 10 - 3/8 +.02, -.03 +.02, -.04 +.04, -.06 +.06, -.10 +.10, -.18
7/16 & 1/2  +.02, -.03 +.04, -.05 +.06, -.08 +.08, -.10 +.12, -.18
9/16 - 3/4  +.02, -.03 +.06, -.08 +.08, -.10 +.10, -.10 +.14, -.18
7/8 & 1   +.08, -.10 +.10, -.14 +.12, -.16 +.16, -.20
1-1/8 - 1-1/2   +.12, -.12 +.16, -.16 +.18, -.18 +.22, -.22

 

- Length of a carriage bolt is measured from the underhead bearing surface to the extreme end of the bolt.

-Tolerance on #10 through 1/2" sizes for nominal lengths of 7/8" and shorter shall be +.031 and -.000

Carriage Bolt: Round Head, Ribbed Neck Properties
Description A round head bolt with a ribbed or serrated shoulder made from low carbon steel.
Applications For use in soft, ductile metals, wood and plastics to keep the bolt from turning when the nut is being tightened.
Material
Carbon Steel - Carbon: .55% max, Phosphorus: .048% max, Sulfur: .058% max
Hardness Rockwell B70-B100
Tensile Strength 60,000 psi min.
Yield Strength 36,000 psi min.
Elongation 18% min
Reduction of Area 35% min

 

  

 Carriage Bolts: Fin Neck


Carriage Bolts Fin Neck Drawing

Carriage Bolts: Fin Neck (ASME B18.5-1990)

Nominal Size or Basic Bolt Diameter

 
Body Diameter (D)

Head Diameter (W) Head Height (H) Fin Thickness (T) Distance Across Fins (A)
Fin Depth (F) Fillet Radius (R)
Max Min  Max  Min  Max Min  Max Min Max Min Max Min Max Min
No 10 .1900 .199 .182 .469 .438 .114 .094 .098 .078 .395 .375 .088 .076 .031 .015
1/4 .2500 .260 .237 .594 .563 .145 .125 .114 .094 .458 .438 .104 .094 .031 .015
5/16 .3125 .324 .298 .719 .688 .176 .156 .145 .125 .551 .531 .135 .125 .031 .015
3/8 .3750 .388 .360 .844 .782 .208 .188 .161 .141 .645 .625 .151 .141 .031 .015
7/16 .4375 .452 .421 .969 .907 .239 .219 .192 .172 .739 .719 .182 .172 .031 .015
1/2 .5000 .515 .483 1.094 1.032 .270 .250 .208 .188 .833 .813 .198 .188 .031 .015

 

Carriage Bolts: Fin Neck: Tolerance on Length
Nominal Bolt Size
Nominal Bolt Length
Up to 1" Over 1" - 2-1/2" Over 2-1/2" - 4"  Over 4" - 6" Longer than 6"
No. 10 - 3/8 +.02, -.03 +.02, -.04 +.04, -.06 +.06, -.10 +.10, -.18
7/16 & 1/2  +.02, -.03 +.04, -.05 +.06, -.08 +.08, -.10 +.12, -.18

 

Carriage Bolt: Fin Neck Properties
Description A round head bolt with a flat bearing surface which intersects with the shank at a 90 degree angle. Where the bearing surface and shank meet are two fins, 180 degrees opposite each other. The bolt is made from low carbon steel.
Applications For use in thin plywood to keep the bolt from turning when nut is being tightened.
Material
Carbon Steel - Carbon: .55% max, Phosphorus: .060% max, Sulfur: .150% max
Hardness Rockwell B69-B100
Tensile Strength 60,000 psi min.
Yield Strength 36,000 psi min.
Elongation 18% min
Reduction of Area 35% min

 

 Carriage Bolts: Flat Head, Square Neck


Carriage Bolt Flat Head Drawing

Carriage Bolts: Flat Head, Square Neck

Bolt Diameter & Thread Pitch

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Head Diameter (A)

Head Height (T) Square Width (O) Square Depth (D)
Max Min  Max  Min  Max Min  Max Min
1/4-20 .640 .590 .098 .078 .260 .245 .156 .125

 

Carriage Bolts: Flat Head, Square Neck: Tolerance on Length
Nominal Bolt Size
 
No. 10 - 3/8 +.02, -.04

 

Carriage Bolt: Flat Head, Square Neck
Description A flat head bolt with a bearing surface that is countersunk to a 150 degree angle. Although flat, the head has a measurable side height causing it to protrude above its mating surface when it is completely tightened. Directly below the head is a square neck and a threaded section that has a unified thread pitch.
Applications The square neck design keeps the bolt from turning as a nut is tightened. The flat head feature gives a lower profile on the front or top side of the fastening than a round head carriage bolt. Designed specifically, but not exclusively for the garage door industry.
Material

Grade-2: AISI 1006-1025 Steel; Grade-5: AISI 1030-1055 Steel

Core Hardness Grade-2: Rockwell B80-B100; Grade-5: Rockwell C25-C34
Tensile Strength Grade-2: 74,000 psi. min.; Grade-5: 120,000 psi. min.
Plating Flat head carriage bolts are usually supplied with a clear zinc finish

Additional Resources

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Carriage Bolts PDF
 
 

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