3/8"-16 Cap Nuts | McMaster-Carr

Filter by

System of Measurement

Material

Nut Type

Cap Nut Profile

Thread Depth

Height

Finish

Corrosion-Resistant Coated

Width

Thread Type

Color

Fastener Strength Grade/Class

Thread Spacing

Locking Type

Performance

Cap Color

Thread Fit

Unified Standard Class 2B

Unified Standard Class 3B

REACH

Compliant

Not Compliant

Export Control Classification Number (ECCN)

EAR99

DFARS Specialty Metals

RoHS

Compliant with Exemptions

Drive Style

Environment

Fastener Strength Rating

Seal Material

Maximum Temperature

34 Products

Cap Nuts

Conceal and protect protruding screw threads while fastening parts together. These nuts help prevent damage to surrounding materials and reduce injuries. Also known as acorn nuts, they have a smooth, rounded head that creates a finished look.

Stainless Steel

Image of Product. Front orientation. Cap Nuts. Cap Nuts.

18-8 Stainless Steel—The choice for wet and outdoor environments, these nuts resist rust. However, they won't hold up to the harsh chemicals that 316 stainless steel can.

Black-Oxide 18-8 Stainless Steel—Typically chosen for their appearance, these nuts have a dark, matte coating. They resist rust in wet and outdoor environments but won't hold up to the harsh chemicals that 316 stainless steel can.

Highly-Corrosion-Resistant 316 Stainless Steel—Our most corrosion-resistant cap nuts, these hold up in just about any environment. They won't degrade from exposure to weather, salt water, and most chemicals.

							Pkg.
	Thread Size	Thread Dp.	Wd.	Ht.	Pkg. Qty.		1-9	10-49	50-Up
18-8 Stainless Steel



		3/8"-16	5/16"	5/8"	1/2"	5	000000000	000000	00000	00000


		3/8"-16	3/8"	9/16"	5/8"	5	000000000	00000	0000	0000


		Black-Oxide 18-8 Stainless Steel



				3/8"-16	3/8"	9/16"	5/8"	1	000000000	0000	0000	0000


				Highly-Corrosion-Resistant 316 Stainless Steel



						3/8"-16	3/8"	9/16"	5/8"	1	000000000	0000	0000	0000

Low-Strength Steel

Rated Grade 2, Class 6, or lower, these nuts are about half as strong as medium-strength steel nuts. They are suitable for light duty fastening applications, such as securing access panels. Use them with screws that have a similar strength rating to avoid stripping threads during installation.

Zinc-Plated Steel—A step up from plain steel, the zinc plating withstands occasional exposure to moisture.

Black Corrosion-Resistant-Coated Steel—Combines a finished appearance with the rust resistance of stainless steel. The coating has been tested to extreme standards, including 1,000 hours of salt spray resistance, to hold up in wet and outdoor environments. Also known as black luster.

Nickel-Plated Steel—This plating resists salt water and chemicals better than zinc plating and is less likely to wear off. It also has a bright, polished appearance.

							Pkg.
	Thread Size	Thread Dp.	Wd.	Ht.	Pkg. Qty.		1-9	10-49	50-Up
Zinc-Plated Steel



		3/8"-16	3/8"	9/16"	5/8"	25	000000000	000000	000000	000000


		Black Corrosion-Resistant-Coated Steel



				3/8"-16	3/8"	9/16"	5/8"	1	000000000	0000	0000	0000


				Nickel-Plated Steel



						3/8"-16	3/8"	5/8"	1/2"	25	000000000	0000	0000	0000

Medium-Strength Steel

About twice as strong as low-strength steel, these Grade 5 nuts fasten most machinery and equipment. To avoid stripped threads during installation, make sure your screw has a comparable strength rating.

Zinc-Plated Steel—A step up from plain steel, the zinc plating withstands occasional exposure to moisture.

								Pkg.
	Thread Size	Thread Dp.	Wd.	Ht.	Fastener Strength Grade/Class	Pkg. Qty.		1-9	10-49	50-Up
Zinc-Plated Steel



		3/8"-16	3/8"	9/16"	5/8"	SAE Grade 5	10	000000000	000000	000000	000000


		Black Corrosion-Resistant-Coated Steel



				3/8"-16	3/8"	9/16"	5/8"	SAE Grade 5	1	000000000	0000	0000	0000

High-Strength Steel

Rated Grade 8 or Class 10, these nuts are about 25% stronger than medium-strength steel nuts. They are commonly used to fasten components in valves, pumps, motors, and other high-stress applications. To avoid stripped threads during installation, make sure your screw has a comparable strength rating.

Zinc-Plated Steel—A step up from plain steel, the zinc plating withstands occasional exposure to moisture.

								Pkg.
	Thread Size	Thread Dp.	Wd.	Ht.	Fastener Strength Grade/Class	Pkg. Qty.		1-9	10-49	50-Up
Zinc-Plated Steel



		3/8"-16	3/8"	9/16"	5/8"	SAE Grade 8	10	000000000	000000	000000	000000


		Black Corrosion-Resistant-Coated Steel



				3/8"-16	3/8"	9/16"	5/8"	SAE Grade 8	1	000000000	0000	0000	0000

Plastic

Nylon 6/6—Slippery and abrasion resistant, these nuts thread on smoothly and stand up to daily wear and tear. Nylon will swell and weaken when exposed to moisture, so it's best for dry environments.

								Pkg.
	Thread Size	Wd.	Ht.	Temp. Range, ° F	Choose a Color	Pkg. Qty.		1-9	10-49	50-Up
Nylon 6/6



		3/8"-16	9/16"	5/8"	-40 to 185	Black , Off-White	25	000000000	000000	000000	00000

Lightweight Aluminum

2011 Aluminum—One-third the weight of steel, these nuts are commonly used in robotics, automation, and other applications that have weight limitations. They're an alternative to stainless steel for rust resistance but are not as strong.

							Pkg.
	Thread Size	Thread Dp.	Wd.	Ht.	Pkg. Qty.		1-9	10-49	50-Up
2011 Aluminum



		3/8"-16	1/4"	5/8"	1/2"	10	000000000	000000	00000	00000

Brass

Brass—Conductive and nonmagnetic, brass nuts are commonly used to secure electrical equipment, such as circuit board assemblies and mounting brackets, inside enclosures. They're also softer than most metals, so they won't damage other fastening components.

Nickel-Plated Brass—In addition to creating a polished appearance, the nickel plating offers better corrosion resistance than plain brass to stand up to solvents and mild chemicals.

Chrome-Plated Brass—The brightest, shiniest finish we offer, this plating has a mirror-like appearance that's often used in decorative applications. It has better corrosion resistance than plain brass to stand up to solvents and mild chemicals.

							Pkg.
	Thread Size	Thread Dp.	Wd.	Ht.	Pkg. Qty.		1-9	10-49	50-Up
Brass



		3/8"-16	1/4"	5/8"	1/2"	10	000000000	000000	00000	00000


		Nickel-Plated Brass



				3/8"-16	1/4"	5/8"	1/2"	10	000000000	00000	00000	0000


				Chrome-Plated Brass



						3/8"-16	1/4"	5/8"	1/2"	5	000000000	0000	0000	0000

High-Profile Cap Nuts

Three times the thread depth of standard cap nuts, these cover and protect extra-long, protruding screws, so you don't have to cut them when fastening parts together. They help prevent damage to surrounding materials and reduce injuries. Also known as acorn nuts, they have a smooth, rounded head that creates a finished look.

Stainless Steel

18-8 Stainless Steel—The choice for wet and outdoor environments, these nuts resist rust. However, they won't hold up to the harsh chemicals that 316 stainless steel can.

	Thread Dp.	Wd.	Ht.		Each
18-8 Stainless Steel



	3/8"-16	3/4"	9/16"	1 1/16"	000000000	000000


	3/8"-16	1"	9/16"	1 5/16"	000000000	00000
	3/8"-16	1 1/4"	9/16"	1 9/16"	000000000	00000

High-Heavy-Profile Cap Nuts

20% wider and taller than standard cap nuts, these have high, flat sides so your wrench won't slip off as you tighten. They cover screws to protect the threads and to prevent damage to surrounding materials. Also known as acorn nuts, they have a smooth, rounded head to create a finished look.

Stainless Steel

18-8 Stainless Steel—The choice for wet and outdoor environments, these nuts resist rust. However, they won't hold up to the harsh chemicals that 316 stainless steel can.

	Thread Dp.	Wd.	Ht.		Each
18-8 Stainless Steel



	3/8"-16	15/32"	3/4"	3/4"	000000000	00000

Steel

Black-Oxide Steel—Typically chosen for their appearance, these nuts have a dark, matte coating. They offer minimal corrosion resistance, so they're best for dry environments.

	Thread Dp.	Wd.	Ht.		Each
Black-Oxide Steel



	3/8"-16	15/32"	3/4"	3/4"	000000000	00000

Cap Nuts with Threadlocker

These nuts not only conceal and protect protruding screw threads, they also resist loosening from mild vibration. They have a nylon patch bonded to their threads that grips screws for a tighter hold than standard cap nuts. They’re reusable a handful of times, but the patch’s holding power decreases with each use. Also known as acorn nuts, they have a smooth, rounded head that creates a finished look.

Stainless Steel

18-8 Stainless Steel—The choice for wet and outdoor environments, these nuts resist rust. However, they won't hold up to the harsh chemicals that 316 stainless steel can.

	Thread Dp.	Wd.	Ht.	Pkg. Qty.		Pkg.
18-8 Stainless Steel



	3/8"-16	3/8"	9/16"	5/8"	5	000000000	000000


	Highly-Corrosion-Resistant 316 Stainless Steel



			3/8"-16	3/8"	9/16"	5/8"	1	000000000	0000

Sanitary Cap Nuts

With extremely smooth sides and rounded edges, these nuts are free of crevices where bacteria can grow. Use them to cover and protect exposed threads while fastening parts together. Nuts are certified by EHEDG to meet sanitary design standards. They have a Buna-N seal on the base that keeps liquid, debris, and other contaminants off the threads. The seal is made with metal and chemical additives, so you can find it with a metal detector or X-ray machine if it falls into your line. Also known as acorn nuts, these have a domed head to create a finished look.

Stainless Steel

Image of Product. Front orientation. Cap Nuts. Sanitary Cap Nuts.

Highly-Corrosion-Resistant 316 Stainless Steel—Won't corrode from frequent washdowns and can stand up to the harshest cleaners and detergents.

	Thread Dp.	Wd.	Ht.	Seal Material	Certification	Food Industry Std.		Each
Highly-Corrosion-Resistant 316 Stainless Steel



	3/8"-16	5/16"	9/16"	15/32"	Buna-N	EHEDG Certified	FDA Compliant 21 CFR 177.2600	000000000	000000

Nylon-Insert Cap Nuts

Get the protection of a cap nut with the vibration resistance of a locknut. These nuts not only conceal protruding screw threads, they also have a nylon insert that grips the screw to prevent loosening from moderate vibration. However, the insert may become brittle if exposed to high temperatures. Nuts are reusable a handful of times, but their holding power decreases with each use.

Low-Strength Steel

Rated Grade 2, Class 6, or lower, these nuts are about half as strong as medium-strength steel nuts. Use them with screws that have a similar strength rating to avoid stripping threads during installation.

Zinc-Plated Steel—A step up from plain steel, the zinc plating withstands occasional exposure to moisture.

Nylon 6/6 Cap—The nylon cap on these nuts is softer than metal, so it's less likely to scratch surrounding surfaces or parts.

	Thread Dp.	Wd.	Ht.	Fastener Strength Grade/Class	Insert Max. Temp., ° F	Pkg. Qty.		Pkg.
Zinc-Plated Steel with Nylon 6/6 Cap



	3/8"-16	21/64"	9/16"	5/8"	SAE Grade 2	250	25	000000000	000000

Cap Nut Assortments

With a range of sizes on hand, you can use these assortments to conceal and protect protruding screw threads while fastening a variety of parts. Also known as acorn nuts, they have a smooth, rounded head that creates a finished look.

Nickel-Plated Steel—This plating resists salt water and chemicals better than zinc plating and is less likely to wear off. It also has a bright, polished appearance.

18-8 Stainless Steel—The choice for wet and outdoor environments, these nuts resist rust. However, they won't hold up to the harsh chemicals that 316 stainless steel can.

	No. of Pieces	Container Type		Each
Nickel-Plated Steel



	6-32, 8-32, 10-32, 1/4"-20, 5/16"-18, 3/8"-16	200	Plastic Box	000000000	000000


	18-8 Stainless Steel



			6-32, 8-32, 10-32, 1/4"-20, 5/16"-18, 3/8"-16	200	Plastic Box	000000000	000000

Open-End Cap Nuts

The open top allows threads to stick out slightly, so you don't have to worry about picking the wrong thread depth. These nuts also engage more threads than standard nuts for a tighter hold. The smooth, curved head creates a finished look, while still partially concealing and protecting the sides of the screw from damage.

Stainless Steel

18-8 Stainless Steel—The choice for wet and outdoor environments, these nuts resist rust. However, they won't hold up to the harsh chemicals that 316 stainless steel can.

	Thread Dp.	Wd.	Ht.		Each
18-8 Stainless Steel



	3/8"-16	3/8"	11/16"	3/8"	000000000	00000

Distorted-Thread Cap Nuts

For a stronger hold than nylon-insert cap nuts, these have irregularly shaped threads that grip the screw to resist loosening. The threads prevent the nut from backing out in high-vibration applications, but they also increase the effort to install and remove. To get these nuts off, you may need special tools, such as an impact wrench or propane torch. They have a smooth, rounded head that conceals and protects protruding screw threads while creating a finished look. Nuts are not reusable.

Stainless Steel

18-8 Stainless Steel—The choice for wet and outdoor environments, these nuts resist rust. However, they won't hold up to the harsh chemicals that 316 stainless steel can.

	Thread Dp.	Wd.	Ht.	Pkg. Qty.		Pkg.
18-8 Stainless Steel



	3/8"-16	3/8"	9/16"	5/8"	5	000000000	000000


	Highly-Corrosion-Resistant 316 Stainless Steel



			3/8"-16	3/8"	9/16"	5/8"	1	000000000	0000

Low-Strength Steel

Zinc-Plated Steel—A step up from plain steel, the zinc plating withstands occasional exposure to moisture.

	Thread Dp.	Wd.	Ht.	Fastener Strength Grade/Class	Pkg. Qty.		Pkg.
Zinc-Plated Steel



	3/8"-16	27/64"	9/16"	5/8"	SAE Grade 2	25	000000000	000000

Sealing Cap Nuts

Keep liquid, gas, debris, and other contaminants from seeping into or out of machinery, with no need for a separate O-ring. These nuts are often used outdoors to protect enclosures and other equipment from harsh weather. They also withstand high pressure, so they are useful for sealing pneumatic pumps and pressure valves. Also known as acorn nuts, they conceal protruding screw threads while fastening parts together and have a smooth, rounded head for a finished look.

Stainless Steel

18-8 Stainless Steel—The choice for wet and outdoor environments, these nuts resist rust. However, they won't hold up to the harsh chemicals that 316 stainless steel can.

	Thread Dp.	Wd.	Ht.	Seal Material	Seal Temp. Range, ° F	Max. Pressure, psi		Each
18-8 Stainless Steel



	3/8"-16	3/8"	5/8"	5/8"	Silicone Rubber	-80 to 400	1,200	000000000	00000

Battery Terminal Covers

For Stud

Terminals

Cover battery terminals to protect against corrosion and dirt.

	Thread Size	Material	Color (For Terminal Polarity)		Each
For Stud Terminals



	Screw On	3/8"-16	Stainless Steel	Black (Negative)	00000000	00000


	Screw On	3/8"-16	Stainless Steel	Red (Positive)	00000000	0000