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Hex Cap Screws Technical Specification Data

Hex Cap Screws are a common fastener used in construction and machine assemblies. They feature a six-sided hexagonal head with a washer face on the bearing surface and a chamfered point. Hex cap screws must meet specific tolerances as described under ASME B18.2.1-1996. The most common specifications for hex head cap screws include ASTM A449 & SAE J429: Grade 2, Grade 5 & Grade 8.

Hex cap screws are commonly mistaken for hex bolts, but differ in many way, including the way they are installed. Bolt are technically installed by turning a nut to tighten the fastener, while cap screws are installed into tapped holes by turning the head to assemble and tighten. Another difference is the washer face that hex cap screws feature on the bearing surface and the chamfered point. While hex bolts have neither the washer face or chamfered point. These 2 fasteners also differ in the applications that they are manufactured for. Hex cap screws are commonly used for precision applications where a tight tolerance is required. Hex bolts are often used in the construction industry where the mechanical properties are more important than dimensional tolerances.

Hex Cap Screw Material Overview

Grade 2 Hex Cap Screw Head Grade 5 Hex Cap Screw Head Grade 8 Hex Cap Screw Head
Grade 2 Hex Cap Screws Grade 5 Hex Cap Screws Grade 8 Hex Cap Screws
Often referred to as “hardware” quality, these fasteners are typically made of low carbon steel. They are ideally suited for holding wood pieces together (in combination with appropriate nuts and washers) or general hardware use where higher strength is not required. There is no grade marking on the head of Grade 2 fasteners, although many manufacturers will put a distinguishing company identification on the head. Tempered Grade 5 fasteners are made of medium carbon steel. These fasteners are then quenched and tempered for the additional strength necessary for most automotive uses and other applications where strength is a moderate concern. The grade marking on the head of a Grade 5 fastener is three equally-spaced lines coming out from the center of the head. Manufacturers’ identifications are added for tracability. Tempered Grade 8 fasteners are manufactured of medium carbon alloy steel for the most demanding applications. These fasteners are then quenched and tempered to superior strength and hardness qualities. The grade marking on a Grade 8 fastener is six equally-spaced lines coming out from the center of the head. The manufacturers’ identifications are added for tracability.
18-8 Stainless Steel Hex Cap Screw Head 316 Stainless Steel Hex Cap Screw Head
18-8 Stainless Steel Hex Cap Screws 316 Stainless Steel Hex Cap Screws 410 Stainless Steel Hex Cap Screws
This is the most popular type of stainless used in the production of fasteners. Its composition is approximately 18% chromium and 8% nickel, thus the name 18-8. Several grades of stainless are included in this classification including 302, 303, 304 and 305. These all have good strength and corrosion resistance. This is more corrosion resistant than 18-8, but also more expensive. It is composed of approximately 18% chromium and 12% nickel with the addition of 2% to 4% molybdenum. It also maintains its strength at higher temperatures than 18-8. It has approximately 12% chromium with no nickel. It is not very corrosion resistant and is magnetic, but it can be heat treated to become harder.

Hex Head Cap Screw Head & Thread Dimensions

Technical dimensional information for the head & threads of hex cap screws of all grades & materials. Technical dimensions include: body diameter, width across the flats, width across the corners, head height, thread length & transition thread lengths.

Hex Head Cap Screw Tolerance on Length

Technical information about the tolerance on length of hex cap screws for all grades and materials.

Hex Head Cap Screw External Thread Dimensions

Technical information of the external thread dimensions of all grades & materials of hex cap screws.

Grade / Material Specific Specifications

Grade 2 Hex Cap Screw Specifications

Description A low or medium carbon steel, externally threaded mechanical device 1/4" diameter or larger, with a trimmed hex head and a washer face on the bearing surface.
Applications/Advantages Economical for use in non-critical applications where the fastener is not subject to extreme temperatures or stress beyond the limits listed herein.
Material ASI 1006 - 1050 or equivalent steel.
Hardness 1/4 through 3/4 in. diameter, 6 in. and shorter in length: Rockwell 880 - B100.
1/4 through 3/4 in. diameter; over 6 in. in length: Rockwell 870 - B100.
7/8 through 1-1/2 in. diameter; all lengths: Rocknell 870 - B100.
Proof Load 1/4 through 3/4 in. diameter, 6 in. and shorter in length: 55,000 psi.
1/4 through 3/4 in diameter, over 6 in. in length: 33,000 psi.
7/8 through 1-1/2 in. diameter, all lengths: 33,000 psi.
Yield Strength* 1/4 through 3/4 in. diameter, 6 in. and shorter in length: 57,000 psi. minmum.
1/4 through 3/4 in. diameter; over 6 in. in length: 86,000 psi. minimum.
7/8 through 1-1/2 in. diameter, all lengths: 36,000 psi. minimum.
Tensile Strength 1/4 through 3/4 in. diameter, 6 in. and shorter in length: 74,000 psi. minimum.
1/4 through 3/4 in. diameter; over 6 in. in length: 60,000 psi. minimum.
7/8 through 1-1/2 in. diameter, all lengths: 60,000 psi. minimum.
Elongation* 18% minimum (all diameters)
Reduction of Area* 85% minimum (all sizes)
Plating See Appendix-A for plating information

*These properties are tested only on machined specimens when the testing machine cannot provide for full testing of the parts.

Grade 2 Hex Head Cap Screw Load Strength

Grade 5 Hex Cap Screw Specifications

Description A cap screw made from medium carbon steel and heat-treated.
Applications/Advantages Has greater tensile strength than a Grade-2. Meld-to-tensile ratio is the lowest of all heat treated steels.
Heat Treatment Grade-5 cap screws shall be heat treated, Oil or water quenched, at the option of the manufacturer, and tempered at a minimum tempering temperature of 800 degrees F.
Material Medium carbon steel. Use of an alloy steel is also acceptable.
Core Hardness 1/4 through 1 in. diameter, all lengths: Rockwell 025 - C34.
1-1/8 through 1-1/2 in. diameter, all lengths: Rockwell C19 - CSO.
Surface Hardness 1/4 through 1 in. diameter, all lengths: Rockvvell 30N54 maximum.
1-1/8 through 1-1/2 in. diameter; all lengths: Rockvvell 30N50 maximum.
Proof Load 1/4 through 1 in. diameter; all lengths: 85,000 psi.
1-1/8 through 1-1/2 in. diameter; all lengths: 74,000 psi.
Yield Strength* 1/4 through 1 in. diameter; all lengths: 92,000 psi. minimum
1-1/8 through 1-1/2 in. diameter; all lengths: 81 ,COO psi. minimum
Tensile Strength 1/4 through 1 in. diameter; all lengths: 120,000 psi. minimum
1-1/8 through 1 1/2 in. dameter, all lengths: 105,000 psi. minimum
Elongation* 14% minimum (all diameters)
Reduction of Area* 35% minimum (all sizes)
Plating See Appendix-A for plating information.

*These properties are tested only on machined specimens when the testing machine cannot provide for full testing of the parts.

Grade 8 Hex Cap Screw Specifications

Description A cap screw made from medium carbon alloy steel and heat-treated.
Applications/Advantages Has greater tensile strength than a Grade-5. Designed for use in high stress applications. See specifications below for more information on how the Grade-8 exceeds the strength of a Grade-5.
Heat Treatment Grade-8 cap screws shall be heat-treated, oil-quenched and tempered at a minimum temperature of 800 degrees F.
Material Medium carbon alloy steel. Note: For diameters 1/4 through 7/16 inch, it is permissible to use AISI 1541 steel.
Core Hardness 1/4 through 1-1/2 in. diameter, all lengths: Rockwell C33 - C39.
Surface Hardness 1/4 through 1-1/2 in. diameter; all lengths: Rockwell 30N58.6 maximum.
Proof Load 1/4 through 1-1/2 in. diameter; all lengths: 120,000 psi.
Yield Strength* 1/4 through 1-1/2 in. diameter; all lengths: 180,000 psi. mnimum
Tensile Strength 1/4 through 1-1/2 in. diameter; all lengths: 150,000 psi. mnimum
Elongation* 12% mnimum (all diameters)
Reduction of Area* 35% mnimum (all sizes)
Plating See Appendix-A for plating information.

*These properties are tested only on machined specimens when the testing machine cannot provide for full testing of the parts.

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18-8 Stainless Steel Hex Cap Screw Specifications

Description 18-8 stainless steel cap screws are made from austenitic alloys as described below.
Applications/Advantages Used in products that require general atmospheric corrosion resistance, such as chemical and food-processing equipment.
Some chemical environments may require special corrosion resistant materials and precautions.
Material A cap screw made from one of the following austenitic alloys: 303, 303Se, 304, XM7 , all of which are characterized as having a chromum content of 17-19% and nickel content of 8-10%.
Heat Treatment The austenitic alloys develop ther strength through work hardening during the fastener manufacturing process, as seen from the hardness properties below. The only heat treatment normally available on austenitic stainless alloys is annealing, which is done at approximately 1900 degree F to a dead soft condition and is not normally thermally reversible.
Hardness 1/4 through 5/8 in. diameter: Rockwell 895 C32
3/4 through 1 in. diameter: Rockwell 880 - 032
Yield Strength* 1/4 through 5/8 in. diameter; 2.25D and longer: 65,000 psi. minimum
3/4" (2.25D & longer) & 7/8 through 1 in. diameter (3D & longer): 45,000 psi. minmum
Tensile Strength 1/4 through 5/8 in. diameter, 2.25D and longer: 100,000 - 150,000 psi.
3/4" (2.25D & longer) & 7/8 through 1 in. diameter (3D & longer): 85,000 - 140,000 psi.
Elongation in 4D* 1/4 through 5/8 in. diameter: 20% mnimum; 3/4 through 1 in. diameter: 25% minimum.

*These properties are tested only on machined specimens when the testing machine cannot provide for full testing of the parts.

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316 Stainless Steel Hex Cap Screw Specifications

Description 316 stainless steel cap screws are made from austenitic alloys as described below.
Applications/Advantages The molybdenum content gives this type of stanless even greater corrosion resistance than 18-8 as well as supenor strength at high temperatures.
Some chemical environments may require special corrosion resistant materials and precautions.
Material A cap screw made from 316 stainless steel, an austenitic alloy which differs from 18-8 by its molybdenum content (2-3%) and a higher nickel content (10-14%).
Heat Treatment The austenitic alloys develop ther strength through work hardening during the fastener manufacturing process, as seen from the hardness properties below. The only heat treatment normally available on austenitic stainless alloys is annealing, which is done at approximately 1900 degree F to a dead soft condition and is not normally thermally reversible.
Hardness 1/4 through 5/8 in. diameter: Rockwell 895 C32
3/4 through 1 in. diameter: Rockwell 880 - 032
Yield Strength* 1/4 through 5/8 in. diameter; 2.25D and longer: 65,000 psi. minimum
3/4" (2.25D & longer) & 7/8 through 1 in. diameter (3D & longer): 45,000 psi. minmum
Tensile Strength 1/4 through 5/8 in. diameter, 2.25D and longer: 100,000 - 150,000 psi.
3/4" (2.25D & longer) & 7/8 through 1 in. diameter (3D & longer): 85,000 - 140,000 psi.
Elongation in 4D* 1/4 through 5/8 in. diameter: 20% mnimum; 3/4 through 1 in. diameter: 25% minimum.

*These properties are tested only on machined specimens when the testing machine cannot provide for full testing of the parts.

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Related Terms

  • Yield Strength - the load at which the fastener exhibits a specified elongation at a specific load
  • Tensile Strength - the minimum total load that will fail the fastener
  • Clamp Load - 75% x Proof x Stress Area. Also called the fastener preload or initial load. The “Clamp” Load is the true maximum load of any fastener
  • Proof Load - the load which the fastener must withstand without a permanent set
  • Torque Dry - assumes a coefficient of friction of 0.20
  • Torque Lubricated - assumes a coefficient of friction of 0.15
  • Minimum Tensile - minimum load at which the fastener will fail. Minimum safe working load is 4:1
  • A325 - the designation for “structural” Grade 5 bolts which have larger head dimensions