Steel Cap Nuts | McMaster-Carr

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151 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.

Low-Strength Steel

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

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.

Chrome-Plated Steel—The brightest, shiniest finish we offer, this plating has a mirror-like appearance that is often used in decorative applications. It resists salt water and chemicals better than zinc plating and is less likely to wear off.

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



		2-56	5/32"	1/4"	1/4"	—	25	91875A101	00000	00000	00000


		3-48	5/32"	1/4"	1/4"	—	10	91875A281	0000	0000	0000
		4-40	5/32"	1/4"	1/4"	—	50	91875A105	00000	00000	00000
		4-48	5/32"	1/4"	1/4"	—	10	91875A284	0000	0000	0000
		5-40	5/32"	5/16"	11/32"	—	10	91875A321	0000	0000	0000
		6-32	5/32"	5/16"	11/32"	—	50	91875A110	00000	00000	00000
		6-40	5/32"	5/16"	11/32"	—	10	91875A469	0000	0000	0000
		8-32	5/32"	5/16"	11/32"	—	50	91875A115	00000	00000	00000
		8-36	5/32"	5/16"	11/32"	—	10	91875A710	0000	0000	0000
		10-24	3/16"	3/8"	13/32"	—	50	91875A120	00000	00000	00000
		10-32	3/16"	3/8"	13/32"	—	50	91875A125	00000	00000	00000


		1/4"-20	1/4"	7/16"	15/32"	—	25	91875A130	00000	0000	0000
		1/4"-28	1/4"	7/16"	15/32"	—	25	91875A135	00000	0000	0000
		5/16"-18	5/16"	1/2"	17/32"	—	25	91875A140	00000	00000	00000
		5/16"-24	5/16"	1/2"	17/32"	—	25	91875A145	00000	00000	00000
		3/8"-16	3/8"	9/16"	5/8"	—	25	91875A150	00000	00000	00000
		3/8"-24	3/8"	9/16"	5/8"	—	25	91875A155	00000	00000	00000
		7/16"-14	7/16"	5/8"	11/16"	—	20	91875A160	00000	00000	00000
		7/16"-20	7/16"	5/8"	11/16"	—	20	91875A165	00000	00000	00000
		1/2"-13	1/2"	3/4"	13/16"	—	10	91875A170	00000	00000	0000
		1/2"-20	1/2"	3/4"	13/16"	—	10	91875A175	00000	00000	0000


		5/8"-11	5/8"	15/16"	1"	—	5	91875A180	00000	00000	0000
		5/8"-18	5/8"	15/16"	1"	—	5	91875A185	00000	00000	0000
		3/4"-10	3/4"	1 1/16"	1 5/32"	—	1	91875A190	0000	0000	0000
		3/4"-16	3/4"	1 1/16"	1 5/32"	—	1	91875A195	0000	0000	0000
		7/8"-9	7/8"	1 1/4"	1 23/64"	—	1	91875A102	0000	0000	0000
		7/8"-14	7/8"	1 1/4"	1 23/64"	—	1	91875A103	0000	0000	0000
		1"-8	1"	1 7/16"	1 35/64"	—	1	91875A038	0000	0000	0000
		1"-14	1"	1 7/16"	1 35/64"	—	1	91875A104	0000	0000	0000
		1 1/4"-7	1 1/4"	1 13/16"	1 61/64"	—	1	91875A106	00000	00000	00000
		1 1/4"-12	1 1/4"	1 13/16"	1 61/64"	—	1	91875A107	00000	00000	00000


		M4 × 0.7 mm	5.3 mm	7 mm	8 mm	DIN 1587	50	91880A035	00000	00000	00000
		M5 × 0.8 mm	3.7 mm	8 mm	10 mm	DIN 1587	50	91880A037	00000	00000	00000
		M6 × 1 mm	7.7 mm	10 mm	12 mm	DIN 1587	50	91880A045	00000	00000	00000
		M8 × 1.25 mm	10.7 mm	13 mm	15 mm	DIN 1587	25	91880A050	00000	00000	00000
		M10 × 1.5 mm	12.7 mm	17 mm	18 mm	DIN 1587	10	91880A056	00000	0000	0000
		M12 × 1.75 mm	15.7 mm	19 mm	22 mm	DIN 1587	10	91880A060	00000	00000	00000


		Black Corrosion-Resistant-Coated Steel



				4-40	5/32"	1/4"	1/4"	—	10	98667A101	00000	00000	00000


				6-32	5/32"	5/16"	11/32"	—	10	98667A110	00000	00000	00000
				8-32	5/32"	5/16"	11/32"	—	10	98667A130	00000	00000	00000
				10-24	3/16"	3/8"	13/32"	—	5	98667A150	0000	0000	0000
				10-32	3/16"	3/8"	13/32"	—	5	98667A190	0000	0000	0000
				1/4"-20	1/4"	7/16"	15/32"	—	5	98667A210	0000	0000	0000
				5/16"-18	5/16"	1/2"	17/32"	—	5	98667A230	00000	0000	0000
				3/8"-16	3/8"	9/16"	5/8"	—	1	98667A250	0000	0000	0000
7/16"-14				7/16"	5/8"	11/16"	—	1	98667A601	0000	0000	0000
1/2"-13	1/2"			3/4"	13/16"	—	1	98667A102	0000	0000	0000
9/16"-12	9/16"			7/8"	15/16"	—	1	98667A695	0000	0000	0000


5/8"-11	5/8"			15/16"	1"	—	1	98667A706	0000	0000	0000


Nickel-Plated Steel



				6-32	5/32"	5/16"	1/4"	—	100	90532A100	00000	0000	0000


				8-32	5/32"	5/16"	1/4"	—	100	90532A125	00000	0000	0000
				10-24	3/16"	3/8"	5/16"	—	100	90532A150	0000	0000	0000
				10-32	3/16"	3/8"	5/16"	—	100	90532A175	00000	00000	00000
				1/4"-20	1/4"	7/16"	3/8"	—	100	90532A200	00000	00000	00000
				5/16"-18	5/16"	9/16"	15/32"	—	50	90532A225	00000	00000	00000
				3/8"-16	3/8"	5/8"	1/2"	—	25	90532A250	0000	0000	0000
				1/2"-13	1/2"	3/4"	9/16"	—	25	90532A275	00000	00000	00000
				5/8"-11	5/8"	15/16"	13/16"	—	10	90532A300	00000	00000	00000
				3/4"-10	3/4"	1 1/8"	1 1/8"	—	1	90532A325	0000	0000	0000


				Chrome-Plated Steel



						M4 × 0.7 mm	3.9 mm	7 mm	8 mm	DIN 1587	5	91982A200	00000	00000	0000


						M5 × 0.8 mm	5.6 mm	8 mm	10 mm	DIN 1587	5	91982A225	00000	00000	0000
						M6 × 1 mm	5.7 mm	10 mm	12 mm	DIN 1587	5	91982A250	00000	00000	00000
						M8 × 1.25 mm	8.2 mm	13 mm	15 mm	DIN 1587	1	91982A275	0000	0000	0000
						M10 × 1.5 mm	9.7 mm	17 mm	18 mm	DIN 1587	1	91982A300	0000	0000	0000
						M12 × 1.75 mm	12.2 mm	19 mm	22 mm	DIN 1587	1	91982A325	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



		1/4"-20	1/4"	7/16"	15/32"	SAE Grade 5	10	98858A101	00000	00000	00000


		5/16"-18	5/16"	1/2"	17/32"	SAE Grade 5	10	98858A102	00000	0000	0000
		3/8"-16	3/8"	9/16"	5/8"	SAE Grade 5	10	98858A103	00000	00000	00000
		1/2"-13	1/2"	3/4"	13/16"	SAE Grade 5	5	98858A104	00000	00000	00000
		5/8"-11	5/8"	15/16"	1"	SAE Grade 5	1	98858A105	0000	0000	0000
		3/4"-10	3/4"	1 1/8"	1 5/32"	SAE Grade 5	1	98858A106	0000	0000	0000
		7/8"-9	7/8"	1 1/4"	1 23/64"	SAE Grade 5	1	98858A291	00000	00000	00000
		1"-8	1"	1 1/2"	1 35/64"	SAE Grade 5	1	98858A107	00000	00000	00000


		Black Corrosion-Resistant-Coated Steel



				1/4"-20	1/4"	7/16"	15/32"	SAE Grade 5	1	98858A558	0000	0000	0000


				5/16"-18	5/16"	1/2"	17/32"	SAE Grade 5	1	98858A570	0000	0000	0000
				3/8"-16	3/8"	9/16"	5/8"	SAE Grade 5	1	98858A640	0000	0000	0000
				1/2"-13	1/2"	3/4"	13/16"	SAE Grade 5	1	98858A849	00000	00000	00000

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	Specs. Met	Pkg. Qty.		1-9	10-49	50-Up
Zinc-Plated Steel



		1/4"-20	1/4"	7/16"	15/32"	SAE Grade 8	—	10	90100A101	000000	000000	00000


		5/16"-18	5/16"	1/2"	17/32"	SAE Grade 8	—	10	90100A102	00000	00000	00000
		3/8"-16	3/8"	9/16"	5/8"	SAE Grade 8	—	10	90100A103	00000	00000	00000
		1/2"-13	1/2"	3/4"	13/16"	SAE Grade 8	—	1	90100A104	0000	0000	0000
		5/8"-11	5/8"	15/16"	1"	SAE Grade 8	—	1	90100A105	0000	0000	0000
		3/4"-10	3/4"	1 1/8"	1 5/32"	SAE Grade 8	—	1	90100A106	0000	0000	0000
		7/8"-9	7/8"	1 1/4"	1 23/64"	SAE Grade 8	—	1	90100A108	00000	00000	00000
		1"-8	1"	1 1/2"	1 35/64"	SAE Grade 8	—	1	90100A107	00000	00000	00000
		M6 × 1 mm	5.7 mm	10 mm	12 mm	Class 10	DIN 1587	5	99164A101	00000	00000	00000
		M8 × 1.25 mm	8.2 mm	13 mm	15 mm	Class 10	DIN 1587	5	99164A102	00000	00000	00000
		M10 × 1.5 mm	9.7 mm	17 mm	18 mm	Class 10	DIN 1587	1	99164A103	0000	0000	0000


		M12 × 1.75 mm	12.2 mm	19 mm	22 mm	Class 10	DIN 1587	1	99164A104	00000	0000	0000


		Black Corrosion-Resistant-Coated Steel



				1/4"-20	1/4"	7/16"	15/32"	SAE Grade 8	—	1	90767A111	0000	0000	0000


				5/16"-18	5/16"	1/2"	17/32"	SAE Grade 8	—	1	90767A112	0000	0000	0000
				3/8"-16	3/8"	9/16"	5/8"	SAE Grade 8	—	1	90767A113	0000	0000	0000
				1/2"-13	1/2"	3/4"	13/16"	SAE Grade 8	—	1	90767A114	00000	00000	00000

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.

Steel—Best for dry environments since moisture will cause these nuts to rust.

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	Specs. Met	Insert Max. Temp., ° F	Pkg. Qty.		Pkg.
Zinc-Plated Steel



	M4 × 0.7 mm	2.3 mm	7 mm	9.6 mm	Class 6	DIN 986	245	50	90582A111	000000


	M5 × 0.8 mm	3.5 mm	8 mm	10.5 mm	Class 6	DIN 986	245	25	90582A112	0000
	M6 × 1 mm	3.9 mm	10 mm	12 mm	Class 6	DIN 986	245	25	90582A113	0000
	M8 × 1.25 mm	5.2 mm	13 mm	14 mm	Class 6	DIN 986	245	25	90582A114	00000
	M10 × 1.5 mm	6.4 mm	16 mm	18 mm	Class 6	DIN 986	245	10	90582A115	00000
	M12 × 1.75 mm	8.3 mm	18 mm	23 mm	Class 6	DIN 986	245	5	90582A116	0000
	M16 × 2 mm	11.3 mm	24 mm	28 mm	Class 6	DIN 986	245	1	90582A117	0000
	M20 × 2.5 mm	13.5 mm	30 mm	35 mm	Class 6	DIN 986	245	1	90582A118	0000


	Zinc-Plated Steel with Nylon 6/6 Cap



			8-32	9/64"	11/32"	23/64"	SAE Grade 2	—	250	25	98190A130	0000


			10-24	9/64"	3/8"	23/64"	SAE Grade 2	—	250	25	98190A150	0000
			10-32	9/64"	3/8"	23/64"	SAE Grade 2	—	250	25	98190A170	0000
			1/4"-20	7/32"	7/16"	31/64"	SAE Grade 2	—	250	25	98190A190	0000
			5/16"-18	1/4"	1/2"	1/2"	SAE Grade 2	—	250	10	98190A210	0000
			3/8"-16	21/64"	9/16"	5/8"	SAE Grade 2	—	250	25	98190A111	00000


			Steel with Nylon 6/6 Cap



					8-32	9/64"	11/32"	23/64"	SAE Grade 2	—	250	25	98190A112	0000


					10-32	9/64"	3/8"	23/64"	SAE Grade 2	—	250	25	98190A113	0000
					1/4"-20	7/32"	7/16"	31/64"	SAE Grade 2	—	250	25	98190A114	0000
					1/4"-28	7/32"	7/16"	31/64"	SAE Grade 2	—	250	25	98190A115	0000
					5/16"-24	1/4"	1/2"	1/2"	SAE Grade 2	—	250	25	98190A116	0000
					3/8"-24	21/64"	9/16"	5/8"	SAE Grade 2	—	250	25	98190A117	00000

Medium-Strength Steel

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"-24	21/64"	9/16"	5/8"	SAE Grade 5	250	10	98190A270	000000

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.

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



	1/4"-20	3/8"	5/8"	5/8"	90790A175	00000


	5/16"-18	3/8"	5/8"	5/8"	90790A185	0000
	3/8"-16	15/32"	3/4"	3/4"	90790A204	0000
	1/2"-13	19/32"	7/8"	15/16"	90790A216	0000
	5/8"-11	25/32"	1 1/16"	1 3/16"	90790A299	0000
	3/4"-10	29/32"	1 1/4"	1 3/8"	90790A417	00000
	7/8"-9	1 1/16"	1 3/8"	1 5/8"	90790A419	00000

Retaining Caps

1050 Spring Steel

Plastic

Use these caps to hold components in place and protect shaft ends. Install these caps with a hammer or push them into place by hand.

Corrosion-Resistant Coated—Corrosion-resistant-coated finish is more corrosion resistant in wet environments than zinc-plated finish. Also known as black luster.

Nickel Plated—Nickel-plated finish has excellent corrosion resistance and a decorative appearance.

Zinc Plated—Zinc-plated finish is corrosion resistant in wet environments.

	OD	Ht.	Insert Material	Min. Hardness	Temp. Range, ° F	Pkg. Qty.		Pkg.
Black Corrosion-Resistant-Coated 1050 Spring Steel



	1/4"	9/16"	7/32"	Steel	Not Rated	—	5	97036A010	00000


	5/16"	5/8"	1/4"	Steel	Not Rated	—	5	97036A020	0000
	3/8"	3/4"	9/32"	Steel	Not Rated	—	5	97036A030	00000
	1/2"	15/16"	21/64"	Steel	Not Rated	—	5	97036A040	00000


	Nickel-Plated 1050 Spring Steel



			1/4"	1/2"	7/32"	Steel	Rockwell C13	—	25	94803A029	0000


			3/8"	3/4"	9/32"	Steel	Rockwell C13	—	25	94803A031	0000


			Zinc-Plated 1050 Spring Steel



					5/16"	9/16"	19/64"	Steel	Rockwell C44	—	25	94803A320	0000


					1/2"	15/16"	21/64"	Steel	Rockwell C38	—	10	94803A050	0000
					5/8"	1 3/16"	27/64"	Steel	Rockwell C38	—	10	94803A060	0000


					Black Plastic



							5/32"	21/32"	23/64"	Steel	Rockwell C45	-90 to 150	50	90310A325	00000


							3/16"	21/32"	23/64"	Steel	Rockwell C45	-90 to 150	50	90310A335	00000
							1/4"	27/32"	23/64"	Steel	Rockwell C45	-90 to 150	50	90310A345	00000
							5/16"	27/32"	29/64"	Steel	Rockwell C45	-90 to 150	25	90310A355	00000
							3/8"	55/64"	15/32"	Steel	Rockwell C45	-90 to 150	25	90310A378	0000
							7/16"	53/64"	7/16"	Steel	Rockwell C45	-90 to 150	10	90310A372	0000
							1/2"	1 5/16"	41/64"	Steel	Rockwell C45	-90 to 150	10	90310A373	0000
							5/8"	1 5/16"	41/64"	Steel	Rockwell C45	-90 to 150	10	90310A374	0000


							White Plastic



									1/8"	21/32"	23/64"	Steel	Rockwell C45	-90 to 150	10	90310A315	00000


									3/16"	21/32"	11/32"	Steel	Rockwell C45	-90 to 150	25	90310A371	0000
									3/8"	55/64"	15/32"	Steel	Rockwell C45	-90 to 150	25	90310A377	0000


									Red Plastic



											5/16"	55/64"	15/32"	Steel	Rockwell C45	-90 to 150	25	90310A376	0000

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.

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



	6-32	5/32"	5/16"	11/32"	SAE Grade 2	50	90455A110	000000


	8-32	5/32"	5/16"	11/32"	SAE Grade 2	50	90455A120	00000
	10-24	3/16"	3/8"	13/32"	SAE Grade 2	25	90455A130	00000
	10-32	3/16"	3/8"	13/32"	SAE Grade 2	25	90455A140	00000
	1/4"-20	19/64"	7/16"	15/32"	SAE Grade 2	50	90455A160	00000
	5/16"-18	23/64"	1/2"	17/32"	SAE Grade 2	25	90455A170	00000
	3/8"-16	27/64"	9/16"	5/8"	SAE Grade 2	25	90455A180	00000
	1/2"-13	1/2"	3/4"	13/16"	SAE Grade 2	5	90455A150	00000

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.

	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	91987A300	000000