M20 Locknuts | McMaster-Carr

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41 Products

Nylon-Insert Locknuts

Versatile yet economical, these are the most commonly used locknuts. The nylon insert grips the screw to prevent loosening from moderate vibration without damaging threads. However, the insert may become brittle if exposed to high temperatures. These locknuts are reusable a handful of times, but the holding power decreases with each use.

High-Strength Steel

Image of Product. Front orientation. Locknuts. Nylon-Insert Locknuts.

Rated Grade 8, Grade C, or Class 10, these locknuts are about 25% stronger than medium-strength steel nuts. 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.

	Wd., mm	Ht., mm	Fastener Strength Grade/Class	Insert Max. Temp., ° F	Specs. Met	Pkg. Qty.		Pkg.
Zinc-Plated Steel



	M20 × 1.5 mm	30	20	ISO Class 10	220	DIN 985, ISO 10511	1	000000000	00000


	M20 × 2 mm	30	20	ISO Class 10	220	DIN 985, ISO 10511	1	000000000	00000
	M20 × 2.5 mm	30	20	ISO Class 10	220	DIN 985	5	000000000	00000

Medium-Strength Steel

These Grade 5 or Class 8 nuts are your go-to for fastening most machinery and equipment. To avoid stripped threads during installation, make sure your screw has a comparable strength rating.

Zinc-Yellow-Chromate-Plated Steel—With a more durable finish than clear zinc plating, these nuts are suitable for most wet and outdoor environments. However, they won't hold up to the harsh chemicals that stainless steel can.

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

	Wd., mm	Ht., mm	Fastener Strength Grade/Class	Insert Max. Temp., ° F	Specs. Met	Pkg. Qty.		Pkg.
Zinc-Yellow-Chromate-Plated Steel



	M20 × 2.5 mm	30	20	ISO Class 8	220	DIN 985, ISO 10511	5	000000000	00000


	Zinc-Plated Steel



			M20 × 1.5 mm	30	20	ISO Class 8	220	DIN 985, ISO 10511	5	000000000	0000


			M20 × 2 mm	30	20	ISO Class 8	220	DIN 985, ISO 10511	1	000000000	0000
			M20 × 2.5 mm	30	20	ISO Class 8	220	DIN 985, ISO 10511	10	000000000	00000

Low-Strength Steel

Rated Grade 2, Class 6, or lower, these locknuts 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.

	Wd., mm	Ht., mm	Insert Max. Temp., ° F	Pkg. Qty.		Pkg.
Zinc-Plated Steel



	M20 × 2.5 mm	30	22	220	10	000000000	000000

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.

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.

	Wd., mm	Ht., mm	Insert Max. Temp., ° F	Specs. Met	Pkg. Qty.		Pkg.
18-8 Stainless Steel



	M20 × 1.5 mm	30	20	220	DIN 985	1	000000000	000000


	M20 × 2.5 mm	30	20	220	DIN 985	1	000000000	0000


	316 Stainless Steel



			M20 × 2.5 mm	30	20	220	DIN 985	1	000000000	0000

Serrated Flange Nuts

Serrations bite into material for mild vibration resistance while the flange eliminates the need for a separate washer. These nuts are ideal for securing screws in oversized or irregularly shaped holes since the flange covers a larger area than standard nuts. You can use them again and again without sacrificing strength. However, the serrations may mar the surface of your material. Also known as collar nuts.

Medium-Strength Steel

Image of Product. Bottom orientation. Flange Nuts. Serrated Flange Nuts.

Rated Grade 5, Grade F, or Class 8, these nuts are your go-to for fastening 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.

				Flange, mm
	Thread Size	Wd., mm	Ht., mm	Dia.	Thk.	Fastener Strength Grade/Class	Specs. Met	Pkg. Qty.		Pkg.
Zinc-Plated Steel



		M20 × 2.5 mm	30	20	42.8	3	ISO Class 8	DIN 6923, ISO 4161	1	000000000	00000

High-Strength Steel

Rated Grade 8, Grade G, or Class 10, these are about 25% stronger than medium-strength steel nuts. They are commonly used to fasten components in valves, pumps, and motors. 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.

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

				Flange, mm
	Thread Size	Wd., mm	Ht., mm	Dia.	Thk.	Fastener Strength Grade/Class	Specs. Met	Pkg. Qty.		Pkg.
Zinc-Plated Steel



		M20 × 2.5 mm	30	20	42.8	3	ISO Class 10	DIN 6923	1	000000000	00000


		Steel



				M20 × 2.5 mm	30	20	42.8	3	ISO Class 10	DIN 6923	1	000000000	0000

Bearing Locknuts

Carbon Steel

With a nylon insert that grips your threaded shaft or spindle without damaging its threads, these locknuts—also called shaft nuts—hold bearings, bushings, gears, and pulleys prone to vibration tightly in place. They come as one piece, so you can easily clamp them onto your shaft or spindle. But, since they aren’t made entirely of metal, they don’t stand up to heat as well as all-metal locknuts. Slots in their sides mean you can tighten and loosen them with a spanner wrench or spanner socket. Their face is also chamfered to help keep the size and weight of your assembly at a minimum. All meet international standards for bearing locknut dimensions.

Zinc-Plated Carbon Steel—Zinc-plated carbon steel locknuts resist rusting from some moisture, but you shouldn’t use them with salt water or chemicals. They are strong and resist wear, though they don’t stand up to corrosion as well as 303 stainless steel locknuts.

Carbon Steel—All carbon steel locknuts are strong and resist wear, though they don’t stand up to corrosion as well as 303 stainless steel locknuts.

303 Stainless Steel—303 stainless steel locknuts resist corrosion better than carbon steel locknuts but aren’t as strong. They withstand washdowns and chemicals.

Thread Spacing—When choosing your thread spacing, consider the precision of your application. The finer the threads, the more control you have when making adjustments.

	Locknuts												Sockets
	Thread						Carbon Steel		Zinc-Plated Carbon Steel		303 Stainless Steel
	Size	Spacing	OD, mm	Wd., mm	Insert Max. Temp., ° F	Specs. Met		Each		Each		Each		Each
Chamfered Face



		M20 × 1 mm	Extra Fine	32	9.5	210	—	———	0	0000000	000000	———	0	———	0


		M20 × 1 mm	Extra Fine	32	10	160	ISO 2982-2	0000000	000000	———	0	0000000	000000	00000000	0000000
		M20 × 1.5 mm	Extra Fine	32	9.5	210	—	———	0	0000000	00000	———	0	———	0

High-Profile Nylon-Insert Locknuts

Slightly taller than standard-profile locknuts, these have a larger gripping area so your wrench or socket won't slip off as you tighten them. They're often used in vehicles and machinery where fasteners can be difficult to reach. The nylon insert grips the screw to prevent loosening from moderate vibration without damaging threads. However, the insert may become brittle if exposed to high temperatures. These locknuts are reusable a handful of times, but the holding power decreases with each use.

High-Strength Steel

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

	Wd., mm	Ht., mm	Fastener Strength Grade/Class	Insert Max. Temp., ° F	Specs. Met	Pkg. Qty.		Pkg.
Zinc-Plated Steel



	M20 × 2.5 mm	30	22	ISO Class 10	220	DIN 982	1	000000000	00000

Medium-Strength Steel

These Grade 5 or Class 8 nuts are your go-to for fastening 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.

	Wd., mm	Ht., mm	Fastener Strength Grade/Class	Insert Max. Temp., ° F	Specs. Met	Pkg. Qty.		Pkg.
Zinc-Yellow-Chromate-Plated Steel



	M20 × 2.5 mm	32	22	ISO Class 8	220	DIN 982, ISO 7040	5	000000000	000000


	Zinc-Plated Steel



			M20 × 1.5 mm	30	22	ISO Class 8	220	DIN 982, ISO 7040	1	000000000	0000


			M20 × 2.5 mm	30	22	ISO Class 8	220	DIN 982, ISO 7040	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.

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.

	Wd., mm	Ht., mm	Insert Max. Temp., ° F	Specs. Met	Pkg. Qty.		Pkg.
18-8 Stainless Steel



	M20 × 2.5 mm	30	22	220	DIN 982	1	000000000	00000


	316 Stainless Steel



			M20 × 2.5 mm	30	22	220	DIN 982	1	000000000	0000

Thin-Profile Nylon-Insert Locknuts

About half the height of standard-profile locknuts, 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 nylon insert grips the screw to prevent loosening from moderate vibration without damaging threads. However, the insert may become brittle if exposed to high temperatures. These locknuts are reusable a handful of times, but the holding power decreases with each use.

Low-Strength Steel

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

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



	M20 × 2.5 mm	30	14.9	245	ISO 10511	1	000000000	00000

Top-Lock Distorted-Thread Locknuts

Irregularly shaped threads at the top of these locknuts grip the screw for a stronger hold than nylon-insert locknuts. Although the threads prevent the nut from backing out due to vibration, 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. Nuts are not reusable.

High-Strength Steel

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

Black-Phosphate-Coated Steel—The dark coating creates both a finished appearance and a barrier against rust that's comparable to zinc yellow-chromate plating.

	Wd., mm	Ht., mm	Fastener Strength Grade/Class	Pkg. Qty.		Pkg.
Zinc-Yellow-Chromate-Plated Steel



	M20 × 2.5 mm	30	20	ISO Class 10	5	000000000	000000


	Zinc-Plated Steel



			M20 × 1.5 mm	30	20	ISO Class 10	5	000000000	00000


			M20 × 2.5 mm	30	20	ISO Class 10	5	000000000	00000


			Black-Phosphate-Coated Steel



					M20 × 2.5 mm	30	20	ISO Class 10	1	000000000	0000

Medium-Strength Steel

These Grade 5 or Class 8 nuts are your go-to for fastening 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.

	Wd., mm	Ht., mm	Fastener Strength Grade/Class	Specs. Met	Pkg. Qty.		Pkg.
Zinc-Plated Steel



	M20 × 1.5 mm	30	20	ISO Class 8	DIN 980V	1	000000000	00000


	M20 × 2.5 mm	30	20	ISO Class 8	DIN 980V	5	000000000	00000

Distorted-Thread Flange Nuts

The strongest hold of all the flange nuts we offer, these have irregularly shaped threads that grip the screw to resist loosening. The threads prevent the nut from backing out due to high vibration, 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, so they are not reusable. Nuts have a flange that distributes pressure evenly across the mounting surface without the need for a separate washer. They are ideal for securing screws in oversized or irregularly shaped holes since the flange covers a larger area than standard nuts. Also known as collar nuts.

High-Strength Steel

Image of Product. Bottom orientation. Flange Nuts. Distorted-Thread Flange Nuts.

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

				Flange, mm
	Thread Size	Wd., mm	Ht., mm	Dia.	Thk.	Fastener Strength Grade/Class	Specs. Met	Pkg. Qty.		Pkg.
Zinc-Plated Steel



		M20 × 2.5 mm	30	22.4	42.8	3	ISO Class 10	DIN 6927, EN 1664, ISO 7044	1	0000000	00000

Nylon-Insert Flange Nuts

A nylon insert grips the screw for a stronger hold than a serrated flange, without damaging threads or marring the surface of your material. However, the insert may become brittle if exposed to high temperatures. These nuts have a flange that distributes pressure evenly across the mounting surface, so you don't need a separate washer. They are ideal for securing screws in oversized or irregularly shaped holes since the flange covers a larger area than standard nuts. You can reuse them a handful of times, but their holding power will decrease with each use. Also known as collar nuts.

Medium-Strength Steel

Image of Product. Front orientation. Flange Nuts. Nylon-Insert Flange Nuts.

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

				Flange, mm
	Thread Size	Wd., mm	Ht., mm	Dia.	Thk.	Fastener Strength Grade/Class	Specs. Met	Insert Max. Temp., ° F	Pkg. Qty.		Pkg.
Zinc-Plated Steel



		M20 × 2.5 mm	30	24.8	42.8	3	ISO Class 8	DIN 6926	250	1	000000000	00000

High-Strength Steel

				Flange, mm
	Thread Size	Wd., mm	Ht., mm	Dia.	Thk.	Fastener Strength Grade/Class	Specs. Met	Insert Max. Temp., ° F	Pkg. Qty.		Pkg.
Zinc-Yellow-Chromate-Plated Steel



		M20 × 2.5 mm	30	24.8	42.8	3	ISO Class 10	DIN 6926	250	1	000000000	00000

Steel-Insert Locknuts for Extreme Vibration

The most secure hold of all the locknuts we offer. The tab on the insert stops the nut from rotating, even under extreme vibration. These locknuts are ideal for equipment with constant motion or jarring starts and stops, including conveyors, shakers, and compactors. In fact, they're so secure that they're even used to fasten components on roller coasters. These locknuts are also reusable, but their holding power decreases after the first use, so you should use a new nut for the strongest possible hold.

Medium-Strength Steel

These Grade 5 or Class 8 nuts are your go-to for fastening most machinery and equipment. 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., mm	Ht., mm	Fastener Strength Grade/Class		Each
Steel



	M20 × 2.5 mm	31.75	22.23	ISO Class 8	000000000	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.

	Thread Dp., mm	Wd., mm	Ht., mm	Fastener Strength Grade/Class	Specs. Met	Insert Max. Temp., ° F	Pkg. Qty.		Pkg.
Zinc-Plated Steel



	M20 × 2.5 mm	13.5	30	35	ISO Class 6	DIN 986	245	1	000000000	00000

Locknuts for use with Cotter Pins

Use these locknuts to secure rotating parts subjected to mild vibration, such as the wheels on carts and hand trucks. They’re not recommended for use on parts exposed to high vibration because the pin can shear under prolonged stress. These nuts are reusable, but you'll need a new cotter pin (not included) with each use.

Medium-Strength Steel

These Grade 5 or Class 8 nuts are your go-to for fastening 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.

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

	Wd., mm	Ht., mm	Fastener Strength Grade/Class	For Cotter Pin Dia., mm	Specs. Met	Pkg. Qty.		Pkg.
Zinc-Plated Steel



	M20 × 2.5 mm	30	22	ISO Class 8	4	DIN 935	5	000000000	000000


	Steel



			M20 × 2.5 mm	30	22	ISO Class 8	4	DIN 935	1	000000000	0000

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.

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.

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.

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



	M20 × 2.5 mm	30	26	1	000000000	000000


	316 Stainless Steel



			M20 × 2.5 mm	30	26	1	000000000	00000