M18 Locknuts | McMaster-Carr

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22 Products

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.

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.

	Thread					Zinc-Plated Carbon Steel
	Size	Spacing	OD, mm	Wd., mm	Insert Max. Temp., ° F		Each
Chamfered Face



		M18 × 1 mm	Extra Fine	28	8.5	210	0000000	000000


		M18 × 1.5 mm	Fine	28	10.5	210	0000000	00000

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



	M18 × 1.5 mm	27	18	ISO Class 10	220	DIN 985, ISO 10511	1	000000000	00000


	M18 × 2.5 mm	27	18.5	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



	M18 × 2.5 mm	27	18.5	ISO Class 8	220	DIN 985, ISO 10511	5	000000000	00000


	Zinc-Plated Steel



			M18 × 1.5 mm	27	18.5	ISO Class 8	220	DIN 985, ISO 10511	10	000000000	00000


			M18 × 2.5 mm	27	18.5	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



	M18 × 2.5 mm	27	18.5	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



	M18 × 1.5 mm	27	18	220	DIN 985	1	000000000	000000


	M18 × 2.5 mm	27	18.5	220	DIN 985	1	000000000	0000


	316 Stainless Steel



			M18 × 2.5 mm	27	18.5	220	DIN 985	1	000000000	00000

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



	M18 × 2.5 mm	26	13	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.

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



	M18 × 2.5 mm	27	18	ISO Class 10	5	000000000	000000


	Zinc-Plated Steel



			M18 × 1.5 mm	27	18	ISO Class 10	5	000000000	0000


			M18 × 2.5 mm	27	18	ISO Class 10	5	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



	M18 × 1.5 mm	27	18	ISO Class 8	DIN 980V	1	000000000	00000


	M18 × 2.5 mm	27	18	ISO Class 8	DIN 980V	5	000000000	00000

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



	M18 × 2.5 mm	27	20	ISO Class 10	220	DIN 982	5	000000000	000000

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-Plated Steel



	M18 × 2.5 mm	27	20	ISO Class 8	220	DIN 982, ISO 7040	5	000000000	000000

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.

	Wd., mm	Ht., mm		Each
18-8 Stainless Steel



	M18 × 2.5 mm	27	23.4	000000000	000000

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



	M18 × 2.5 mm	27	21	ISO Class 8	4	DIN 935	1	000000000	00000


	Steel



			M18 × 2.5 mm	27	21	ISO Class 8	4	DIN 935	1	000000000	0000