Flexible Locknuts | McMaster-Carr

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Heavy Vibration Resistant

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Unified Standard Class 3B

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Specifications Met

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185 Products

Performance

Corrosion Resistant

Won't rust in wet and outdoor environments

68 products

Specifications Met

Military Specification

Meet strict U.S. military standards for material and construction

18 products

Hex Nut Profile

Standard

The most common profile of locknut

105 products

Thin

Fit in spaces with low clearance

58 products

Flex-Top Locknuts for Heavy Vibration

The top section of these nuts expands to grip the screw on all sides for a stronger hold than both nylon-insert and distorted-thread locknuts. They’re often used in equipment with constant, vigorous vibration, such as engines. These locknuts are reusable a handful of times, but the holding power decreases with each use.

Steel

These locknuts have equivalent strength to Grade 8 and Class 10 steel nuts. To avoid stripped threads during installation, make sure your screw has a comparable strength rating.

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

Cadmium-Plated Steel—These locknuts have good lubricity to thread on smoothly and ease installation. The plating also creates a barrier against rust that's comparable to zinc-yellow-chromate plating.

	Wd.	Ht.	Pkg. Qty.		Pkg.
Black-Oxide Steel



	1/4"-20	7/16"	19/64"	5	000000000	00000


	1/4"-28	7/16"	5/16"	5	000000000	0000
	5/16"-18	1/2"	23/64"	5	000000000	0000
	5/16"-24	1/2"	23/64"	5	000000000	0000
	3/8"-16	9/16"	15/32"	5	000000000	0000
	3/8"-24	9/16"	15/32"	5	000000000	0000
	7/16"-14	5/8"	15/32"	1	000000000	0000
	1/2"-13	3/4"	39/64"	1	000000000	0000
	1/2"-20	3/4"	39/64"	1	000000000	0000
	5/8"-11	15/16"	49/64"	1	000000000	0000
	5/8"-18	15/16"	49/64"	1	000000000	0000


	3/4"-10	1 1/16"	57/64"	1	000000000	0000
	3/4"-16	1 1/16"	57/64"	1	000000000	0000
	M6 × 1 mm	10 mm	7.8 mm	1	000000000	0000
	M8 × 1.25 mm	13 mm	10.4 mm	1	000000000	0000
	M10 × 1.5 mm	15 mm	13 mm	1	000000000	0000
	M12 × 1.75 mm	19 mm	15.6 mm	1	000000000	0000


	Cadmium-Plated Steel



			4-40	1/4"	5/32"	10	000000000	00000


			6-32	5/16"	3/16"	25	000000000	0000
			8-32	11/32"	1/4"	25	000000000	00000
			10-24	3/8"	1/4"	25	000000000	00000
			10-32	3/8"	1/4"	25	000000000	00000
			1/4"-20	7/16"	19/64"	25	000000000	00000
			1/4"-28	7/16"	5/16"	25	000000000	00000
			5/16"-18	1/2"	23/64"	10	000000000	0000
			5/16"-24	1/2"	23/64"	10	000000000	0000
			3/8"-16	9/16"	15/32"	10	000000000	00000
			3/8"-24	9/16"	15/32"	10	000000000	00000


			7/16"-14	5/8"	15/32"	5	000000000	0000
			7/16"-20	5/8"	15/32"	1	000000000	0000
			1/2"-13	3/4"	39/64"	5	000000000	0000
			1/2"-20	3/4"	39/64"	5	000000000	00000
			9/16"-18	7/8"	31/64"	1	000000000	0000
			5/8"-11	15/16"	49/64"	1	000000000	0000
			5/8"-18	15/16"	49/64"	1	000000000	0000
			3/4"-10	1 1/16"	57/64"	1	000000000	0000
			3/4"-16	1 1/16"	57/64"	1	000000000	0000
			7/8"-9	1 1/4"	1 1/64"	1	000000000	00000


			7/8"-14	1 1/4"	1 1/64"	1	000000000	00000
			1"-8	1 7/16"	1 9/64"	1	000000000	00000
			1"-14	1 7/16"	1 9/64"	1	000000000	00000
			M6 × 1 mm	10 mm	7.8 mm	5	000000000	0000
			M8 × 1.25 mm	13 mm	10.4 mm	1	000000000	0000
			M10 × 1.5 mm	17 mm	13 mm	1	000000000	0000
			M12 × 1.75 mm	19 mm	15.6 mm	1	000000000	0000

Corrosion-Resistant Stainless Steel

18-8 Stainless Steel—The choice for wet and outdoor environments, these locknuts 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 to create a finished look. They resist rust in wet and outdoor environments, but won't hold up to the harsh chemicals that 316 stainless steel can.

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

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



		2-56	1/4"	5/32"	5	000000000	000000


		6-32	5/16"	3/16"	5	000000000	0000
		8-32	11/32"	1/4"	5	000000000	0000
		10-24	3/8"	1/4"	5	000000000	0000
		10-32	3/8"	1/4"	10	000000000	00000
		1/4"-20	7/16"	19/64"	5	000000000	00000
		1/4"-28	7/16"	19/64"	5	000000000	0000
		5/16"-18	1/2"	23/64"	1	000000000	0000
		5/16"-24	1/2"	23/64"	1	000000000	0000
		3/8"-16	9/16"	15/32"	1	000000000	0000
		3/8"-24	9/16"	15/32"	1	000000000	0000


		7/16"-20	5/8"	15/32"	1	000000000	00000
		1/2"-13	3/4"	39/64"	1	000000000	0000
		1/2"-20	3/4"	39/64"	1	000000000	0000
		M3 × 0.5 mm	5.5 mm	4.5 mm	1	000000000	0000
		M4 × 0.7 mm	7 mm	6 mm	1	000000000	0000
		M5 × 0.8 mm	8 mm	7.5 mm	1	000000000	0000
		M6 × 1 mm	10 mm	7.8 mm	1	000000000	0000
		M8 × 1.25 mm	13 mm	10.4 mm	1	000000000	0000
		M10 × 1.5 mm	17 mm	13 mm	1	000000000	00000
		M12 × 1.75 mm	19 mm	15.6 mm	1	000000000	00000


		M14 × 2 mm	22 mm	18.2 mm	1	000000000	00000
		M16 × 2 mm	24 mm	20.8 mm	1	000000000	00000
		M18 × 2.5 mm	27 mm	23.4 mm	1	000000000	00000
		M20 × 2.5 mm	30 mm	26 mm	1	000000000	00000
		M22 × 2.5 mm	32 mm	28.6 mm	1	000000000	00000
		M24 × 3 mm	36 mm	31.2 mm	1	000000000	00000


		Black-Oxide 18-8 Stainless Steel



				8-32	11/32"	1/4"	5	000000000	0000


				10-24	3/8"	1/4"	5	000000000	0000
				10-32	3/8"	1/4"	5	000000000	0000
				1/4"-20	7/16"	19/64"	5	000000000	00000
				3/8"-16	9/16"	15/32"	1	000000000	0000
				1/2"-13	3/4"	39/64"	1	000000000	0000
				1/2"-20	3/4"	39/64"	1	000000000	0000


				316 Stainless Steel



						M3 × 0.5 mm	5.5 mm	4.5 mm	1	000000000	0000


						M4 × 0.7 mm	7 mm	6 mm	1	000000000	0000
						M5 × 0.8 mm	8 mm	7.5 mm	1	000000000	0000
						M6 × 1 mm	10 mm	7.8 mm	1	000000000	0000
						M8 × 1.25 mm	13 mm	10.4 mm	1	000000000	00000
M10 × 1.5 mm						17 mm	13 mm	1	000000000	00000
M12 × 1.75 mm	19 mm					15.6 mm	1	000000000	00000
M20 × 2.5 mm	30 mm					26 mm	1	000000000	00000

Mil. Spec. Flex-Top Locknuts for Heavy Vibration

These locknuts are manufactured and tested to strict U.S. military standards for material and construction. The top section expands to grip the screw on all sides for a stronger hold than both nylon-insert and distorted-thread locknuts. As a result, they're suitable for use in equipment with constant, vigorous vibration, such as engines. These locknuts are reusable a handful of times, but the holding power decreases with each use.

Steel

These locknuts have equivalent strength to Grade 8 and Class 10 steel nuts. To avoid stripped threads during installation, make sure your screw has a comparable strength rating.

	Wd.	Ht.	Mil. Spec.	Pkg. Qty.		Pkg.
Cadmium-Plated Steel



	4-40	1/4"	5/32"	MS21045-04	5	000000000	000000


	6-32	5/16"	3/16"	MS21045-06	5	000000000	0000
	8-32	11/32"	1/4"	MS21045-08	5	000000000	00000
	10-32	3/8"	1/4"	MS21045-3	5	000000000	0000
	1/4"-28	7/16"	5/16"	MS21045-4	5	000000000	00000
	5/16"-24	1/2"	23/64"	MS21045-5	5	000000000	00000
	3/8"-24	9/16"	15/32"	MS21045-6	5	000000000	00000
	7/16"-20	11/16"	15/32"	MS21045-7	1	000000000	00000
	1/2"-20	3/4"	39/64"	MS21045-8	1	000000000	00000
	9/16"-18	7/8"	11/16"	MS21045-9	1	000000000	00000
	5/8"-18	15/16"	49/64"	MS21045-10	1	000000000	00000


	3/4"-16	1 1/16"	57/64"	MS21045-12	1	000000000	00000

Corrosion-Resistant Stainless Steel

Silver-Plated 18-8 Stainless Steel—The choice for wet and outdoor environments, these locknuts won't rust. The silver plating adds lubricity to help them thread on smoothly during installation.

	Wd.	Ht.	Mil. Spec.	Specs. Met	Pkg. Qty.		Pkg.
Silver-Plated 18-8 Stainless Steel



	4-40	1/4"	9/64"	MS21046C04	NASM21046	1	000000000	000000


	6-32	5/16"	11/64"	MS21046C06	NASM21046	1	000000000	00000
	8-32	11/32"	15/64"	MS21046C08	NASM21046	1	000000000	0000
	10-32	3/8"	15/64"	MS21046C3	NASM21046	1	000000000	00000
	1/4"-28	7/16"	9/32"	MS21046C4	NASM21046	1	000000000	00000
	3/8"-24	9/16"	25/64"	MS21046C6	NASM21046	1	000000000	00000

Thin-Profile Flex-Top Locknuts for Heavy Vibration

About two-thirds the height of standard flex-top nuts, these fit in spaces with low clearance. You can also use them as jam nuts by threading them against a hex nut to hold it in place. The top section expands to grip the screw on all sides for a stronger hold than both nylon-insert and distorted-thread locknuts. As a result, they're suitable for use in equipment with constant, vigorous vibration, such as engines. These locknuts are reusable a handful of times, but the holding power decreases with each use.

Steel

These locknuts have equivalent strength to Grade 8 and Class 10 steel nuts. To avoid stripped threads during installation, make sure your screw has a comparable strength rating.

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

	Wd.	Ht.	Pkg. Qty.		Pkg.
Cadmium-Plated Steel



	6-32	5/16"	9/64"	25	000000000	000000


	8-32	11/32"	3/16"	25	000000000	00000
	10-24	3/8"	3/16"	25	000000000	00000
	10-32	3/8"	3/16"	25	000000000	00000
	1/4"-20	7/16"	7/32"	25	000000000	00000
	1/4"-28	7/16"	7/32"	25	000000000	00000
	5/16"-18	1/2"	17/64"	10	000000000	0000
	5/16"-24	1/2"	17/64"	10	000000000	0000
	3/8"-16	9/16"	9/32"	10	000000000	00000
	3/8"-24	9/16"	9/32"	10	000000000	00000
	7/16"-20	5/8"	21/64"	5	000000000	0000


	1/2"-13	3/4"	21/64"	5	000000000	0000
	1/2"-20	3/4"	21/64"	5	000000000	0000
	5/8"-11	15/16"	13/32"	1	000000000	0000
	5/8"-18	15/16"	13/32"	1	000000000	0000
	3/4"-10	1 1/16"	27/64"	1	000000000	0000
	3/4"-16	1 1/16"	27/64"	1	000000000	0000
	7/8"-9	1 1/4"	31/64"	1	000000000	00000
	1"-8	1 7/16"	37/64"	1	000000000	0000
	1"-14	1 7/16"	37/64"	1	000000000	0000
	1 1/4"-12	1 13/16"	49/64"	1	000000000	00000


	1 1/2"-12	2 3/16"	57/64"	1	000000000	00000


	Steel



			6-32	5/16"	9/64"	10	000000000	0000


			8-32	11/32"	3/16"	10	000000000	0000
			10-24	3/8"	3/16"	10	000000000	0000
			10-32	3/8"	3/16"	10	000000000	0000
			1/4"-20	7/16"	7/32"	10	000000000	0000
			1/4"-28	7/16"	7/32"	10	000000000	0000
			5/16"-18	1/2"	17/64"	5	000000000	0000
			5/16"-24	1/2"	17/64"	5	000000000	0000
			3/8"-16	9/16"	9/32"	5	000000000	0000
			3/8"-24	9/16"	9/32"	5	000000000	0000
			1/2"-13	3/4"	21/64"	1	000000000	0000


			1/2"-20	3/4"	21/64"	1	000000000	0000
			5/8"-11	15/16"	13/32"	1	000000000	0000
			5/8"-18	15/16"	13/32"	1	000000000	0000
			3/4"-10	1 1/16"	27/64"	1	000000000	0000
			3/4"-16	1 1/16"	27/64"	1	000000000	0000
			1"-14	1 7/16"	37/64"	1	000000000	0000
			1 1/8"-12	1 5/8"	41/64"	1	000000000	00000
			1 1/4"-12	1 13/16"	49/64"	1	000000000	00000
			1 3/8"-12	1 15/16"	53/64"	1	000000000	00000
			1 1/2"-12	2 3/16"	57/64"	1	000000000	00000

Corrosion-Resistant Stainless Steel

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

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



	6-32	5/16"	9/64"	10	000000000	000000


	8-32	11/32"	3/16"	5	000000000	00000
	10-24	3/8"	3/16"	5	000000000	00000
	10-32	3/8"	3/16"	10	000000000	00000
	1/4"-20	7/16"	7/32"	5	000000000	00000
	1/4"-28	7/16"	7/32"	5	000000000	00000
	5/16"-18	1/2"	17/64"	1	000000000	0000
	5/16"-24	1/2"	17/64"	1	000000000	0000
	3/8"-16	9/16"	9/32"	1	000000000	0000
	3/8"-24	9/16"	9/32"	1	000000000	0000
	1/2"-13	3/4"	21/64"	1	000000000	0000


	1/2"-20	3/4"	21/64"	1	000000000	00000
	5/8"-18	15/16"	13/32"	1	000000000	00000
	3/4"-16	1 1/16"	27/64"	1	000000000	00000
	7/8"-14	1 1/4"	31/64"	1	000000000	00000

Heavy-Profile Flex-Top Locknuts for Heavy Vibration

About 10% wider and taller than standard flex-top nuts, these handle heavier loads by distributing them over a larger area. The top section expands to grip the screw on all sides for a stronger hold than both nylon-insert and distorted-thread locknuts. As a result, they're suitable for use in equipment with constant, vigorous vibration, such as engines. These locknuts are reusable a handful of times, but the holding power decreases with each use.

Steel

These locknuts have equivalent strength to Grade 8 and Class 10 steel nuts. To avoid stripped threads during installation, make sure your screw has a comparable strength rating.

	Wd.	Ht.	Pkg. Qty.		Pkg.
Cadmium-Plated Steel



	1/4"-20	1/2"	19/64"	10	000000000	000000


	5/16"-18	9/16"	21/64"	10	000000000	00000
	3/8"-16	5/8"	25/64"	10	000000000	00000
	1/2"-13	13/16"	1/2"	5	000000000	00000
	5/8"-11	1"	41/64"	1	000000000	0000
	3/4"-10	1 1/8"	49/64"	1	000000000	0000
	7/8"-9	1 5/16"	57/64"	1	000000000	00000
	1"-8	1 1/2"	1 1/64"	1	000000000	00000

Corrosion-Resistant Stainless Steel

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

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



	1/4"-20	1/2"	19/64"	1	000000000	000000


	5/16"-18	9/16"	21/64"	1	000000000	00000
	3/8"-16	5/8"	25/64"	1	000000000	00000
	7/16"-14	3/4"	29/64"	1	000000000	00000
	1/2"-13	13/16"	1/2"	1	000000000	00000

Thin-Heavy-Profile Flex-Top Locknuts for Heavy Vibration

About two-thirds the height of standard flex-top nuts and 10% wider, these fit in spaces with low clearance and handle heavier loads by distributing them over a larger area. Because of the thin profile, you can also use them as jam nuts by threading them against a hex nut to hold it in place. The top section expands to grip the screw on all sides for a stronger hold than both nylon-insert and distorted-thread locknuts. As a result, they're suitable for use in equipment with constant, vigorous vibration, such as engines. These locknuts are reusable a handful of times, but the holding power decreases with each use.

Steel

These locknuts have equivalent strength to Grade 8 and Class 10 steel nuts. To avoid stripped threads during installation, make sure your screw has a comparable strength rating.

	Wd.	Ht.	Pkg. Qty.		Pkg.
Cadmium-Plated Steel



	1/4"-20	1/2"	7/32"	25	000000000	000000


	5/16"-18	9/16"	17/64"	10	000000000	0000
	3/8"-16	5/8"	9/32"	10	000000000	00000
	7/16"-14	3/4"	21/64"	1	000000000	0000
	1/2"-13	13/16"	21/64"	5	000000000	00000
	5/8"-11	1"	13/32"	1	000000000	0000
	3/4"-10	1 1/8"	27/64"	1	000000000	00000
	7/8"-9	1 5/16"	31/64"	1	000000000	00000
	1"-8	1 1/2"	37/64"	1	000000000	00000