Star Hex Nuts | McMaster-Carr

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Washer OD

Minimum Slot Depth

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159 Products

Locking Type

Lock Washer

Twist into place by hand to save on assembly time

61 products

Cotter Pin

Secure rotating parts subjected to mild vibration, such as wheels on carts

98 products

Performance

Corrosion Resistant

Won't rust in wet and outdoor environments

43 products

Hex Nut Profile

Standard

The most common profile of locknut

156 products

Locknuts with External-Tooth Lock Washer

To save on assembly time, these locknuts combine a hex nut with a free-spinning lock washer, so you can twist them into place by hand. Once the nut is against your material surface, tighten it down with a wrench or socket to get the teeth to bite. Although these nuts install more quickly than nylon-insert locknuts, they don't hold up as well against vibration and can mar your material. As long as the washer stays intact, you can reuse them. Also known as Keps and K-lock nuts.

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.

Black-Zinc-Plated Steel—The dark zinc plating withstands occasional exposure to moisture while creating a finished look.

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



	M3 × 0.5 mm	5.5	3.3	ISO Class 8	7.1	100	000000000	000000


	M4 × 0.7 mm	7	4.1	ISO Class 8	8.5	100	000000000	00000
	M5 × 0.8 mm	8	5.2	ISO Class 8	9.5	100	000000000	00000
	M6 × 1 mm	10	6.2	ISO Class 8	12	100	000000000	00000
	M8 × 1.25 mm	13	8.5	ISO Class 8	15.5	25	000000000	0000
	M10 × 1.5 mm	17	9.7	ISO Class 8	20.1	10	000000000	00000


	Black-Zinc-Plated Steel



			M3 × 0.5 mm	5.5	3	ISO Class 8	7.1	100	000000000	00000


			M4 × 0.7 mm	7	4.1	ISO Class 8	8.5	100	000000000	00000
			M5 × 0.8 mm	8	5.2	ISO Class 8	9.5	100	000000000	00000
			M6 × 1 mm	10	6.2	ISO Class 8	12	50	000000000	00000
			M8 × 1.25 mm	13	8.5	ISO Class 8	15.5	25	000000000	00000
			M10 × 1.5 mm	17	9.7	ISO Class 8	20.1	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.

Black-Zinc-Plated Steel—The dark zinc plating withstands occasional exposure to moisture while creating a finished look.

	Wd.	Ht.	Washer OD	Pkg. Qty.		Pkg.
Zinc-Plated Steel



	4-40	1/4"	7/64"	0.281"	100	000000000	00000


	5-40	5/16"	9/64"	0.344"	100	000000000	0000
	6-32	5/16"	9/64"	0.344"	100	000000000	0000
	8-32	11/32"	5/32"	0.375"	100	000000000	0000
	10-24	3/8"	5/32"	0.406"	100	000000000	0000
	10-32	3/8"	5/32"	0.406"	100	000000000	0000
	12-24	7/16"	3/16"	0.5"	50	000000000	0000
	1/4"-20	7/16"	15/64"	0.5"	100	000000000	0000
	1/4"-28	7/16"	15/64"	0.5"	100	000000000	0000
	5/16"-18	1/2"	21/64"	0.578"	100	000000000	00000
	5/16"-24	1/2"	5/16"	0.592"	50	000000000	00000


	3/8"-16	9/16"	25/64"	0.656"	100	000000000	00000
	3/8"-24	9/16"	25/64"	0.656"	100	000000000	00000
	1/2"-13	3/4"	31/64"	0.891"	10	000000000	00000


	Black-Zinc-Plated Steel



			4-40	1/4"	1/8"	0.281"	100	000000000	0000


			6-32	5/16"	9/64"	0.344"	100	000000000	0000
			8-32	11/32"	5/32"	0.375"	100	000000000	0000
			10-24	3/8"	5/32"	0.406"	100	000000000	0000
			10-32	3/8"	5/32"	0.406"	100	000000000	0000
			1/4"-20	7/16"	7/32"	0.5"	100	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.

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.

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



	4-40	1/4"	1/8"	0.281"	100	000000000	00000


	4-48	1/4"	1/8"	0.281"	100	000000000	00000
	6-32	5/16"	9/64"	0.344"	100	000000000	0000
	8-32	11/32"	11/64"	0.375"	100	000000000	00000
	10-24	3/8"	11/64"	0.406"	100	000000000	00000
	10-32	3/8"	11/64"	0.406"	100	000000000	00000
	12-24	7/16"	11/64"	0.5"	50	000000000	00000
	1/4"-20	7/16"	15/64"	0.5"	50	000000000	00000
	1/4"-28	7/16"	15/64"	0.5"	50	000000000	0000
	5/16"-18	1/2"	21/64"	0.578"	25	000000000	0000
	5/16"-24	1/2"	21/64"	0.578"	25	000000000	00000


	3/8"-16	9/16"	25/64"	0.656"	25	000000000	00000
	3/8"-24	9/16"	25/64"	0.656"	10	000000000	0000
	1/2"-13	3/4"	7/16"	0.871"	10	000000000	0000
	M3 × 0.5 mm	5.5 mm	3.3 mm	6.5 mm	50	000000000	00000
	M4 × 0.7 mm	7 mm	4.1 mm	8.2 mm	50	000000000	00000
	M5 × 0.8 mm	8 mm	5.2 mm	9.5 mm	25	000000000	0000
	M6 × 1 mm	10 mm	6.2 mm	11.5 mm	25	000000000	0000
	M8 × 1.25 mm	13 mm	8.5 mm	15.1 mm	5	000000000	0000
	M10 × 1.5 mm	17 mm	9.7 mm	19.2 mm	5	000000000	00000


	Black-Oxide 18-8 Stainless Steel



			M3 × 0.5 mm	5.5 mm	3.3 mm	6.5 mm	25	000000000	0000


			M4 × 0.7 mm	7 mm	4.1 mm	8.2 mm	25	000000000	00000
			M5 × 0.8 mm	8 mm	5.2 mm	9.5 mm	25	000000000	00000
			M6 × 1 mm	10 mm	6.2 mm	11.5 mm	25	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.

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



		1/4"-20	7/16"	7/32"	SAE Grade 5	1/16"	—	25	000000000	000000


		1/4"-28	7/16"	7/32"	SAE Grade 5	1/16"	—	10	000000000	0000
		5/16"-18	1/2"	17/64"	SAE Grade 5	5/64"	—	25	000000000	00000
		3/8"-16	9/16"	21/64"	SAE Grade 5	7/64"	—	25	000000000	00000
		3/8"-24	9/16"	21/64"	SAE Grade 5	7/64"	—	10	000000000	00000
		7/16"-14	11/16"	3/8"	SAE Grade 5	7/64"	—	25	000000000	00000
		7/16"-20	11/16"	3/8"	SAE Grade 5	7/64"	—	10	000000000	0000
		1/2"-13	3/4"	7/16"	SAE Grade 5	7/64"	—	10	000000000	0000
		1/2"-20	3/4"	7/16"	SAE Grade 5	7/64"	—	10	000000000	00000
		9/16"-12	7/8"	31/64"	SAE Grade 5	9/64"	—	10	000000000	00000
		9/16"-18	7/8"	31/64"	SAE Grade 5	9/64"	—	10	000000000	00000


		5/8"-11	15/16"	35/64"	SAE Grade 5	5/32"	—	10	000000000	00000
		5/8"-18	15/16"	35/64"	SAE Grade 5	5/32"	—	10	000000000	00000
		3/4"-10	1 1/8"	41/64"	SAE Grade 5	5/32"	—	5	000000000	00000
		3/4"-16	1 1/8"	41/64"	SAE Grade 5	5/32"	—	5	000000000	00000
		7/8"-14	1 5/16"	49/64"	SAE Grade 5	3/16"	—	1	000000000	0000
		1"-8	1 1/2"	55/64"	SAE Grade 5	3/16"	—	1	000000000	0000
		1"-14	1 1/2"	55/64"	SAE Grade 5	3/16"	—	1	000000000	0000
		1 1/4"-7	1 7/8"	1 3/32"	SAE Grade 5	5/16"	—	1	000000000	0000
		1 1/4"-12	1 7/8"	1 3/32"	SAE Grade 5	5/16"	—	1	000000000	00000
		M6 × 1 mm	10 mm	7.5 mm	ISO Class 8	1.6 mm	DIN 935	5	000000000	0000


		M8 × 1.25 mm	13 mm	9.5 mm	ISO Class 8	2 mm	DIN 935	5	000000000	0000
		M10 × 1.5 mm	17 mm	12 mm	ISO Class 8	2.5 mm	DIN 935	5	000000000	0000
		M12 × 1.5 mm	19 mm	15 mm	ISO Class 8	3.2 mm	DIN 935	5	000000000	0000
		M12 × 1.75 mm	19 mm	15 mm	ISO Class 8	3.2 mm	DIN 935	5	000000000	0000
		M14 × 1.5 mm	22 mm	16 mm	ISO Class 8	3.2 mm	DIN 935	1	000000000	0000
		M14 × 2 mm	22 mm	16 mm	ISO Class 8	3.2 mm	DIN 935	1	000000000	0000
		M16 × 1.5 mm	24 mm	19 mm	ISO Class 8	4 mm	DIN 935	10	000000000	00000
		M16 × 2 mm	24 mm	19 mm	ISO Class 8	4 mm	DIN 935	5	000000000	0000
		M18 × 2.5 mm	27 mm	21 mm	ISO Class 8	4 mm	DIN 935	1	000000000	0000
		M20 × 2.5 mm	30 mm	22 mm	ISO Class 8	4 mm	DIN 935	5	000000000	00000


		M24 × 2 mm	36 mm	27 mm	ISO Class 8	5 mm	DIN 935	1	000000000	0000
		M24 × 3 mm	36 mm	27 mm	ISO Class 8	5 mm	DIN 935	1	000000000	0000
		M27 × 3 mm	41 mm	30 mm	ISO Class 8	5 mm	DIN 935	1	000000000	00000
		M30 × 3.5 mm	46 mm	33 mm	ISO Class 8	6.3 mm	DIN 935	1	000000000	00000


		Steel



				M12 × 1.5 mm	19 mm	15 mm	ISO Class 8	3.2 mm	DIN 935	10	000000000	0000


				M14 × 1.5 mm	22 mm	16 mm	ISO Class 8	3.2 mm	DIN 935	1	000000000	0000
				M14 × 2 mm	22 mm	16 mm	ISO Class 8	3.2 mm	DIN 935	1	000000000	0000
				M16 × 1.5 mm	24 mm	19 mm	ISO Class 8	4 mm	DIN 935	1	000000000	0000
				M16 × 2 mm	24 mm	19 mm	ISO Class 8	4 mm	DIN 935	1	000000000	0000
				M18 × 2.5 mm	27 mm	21 mm	ISO Class 8	4 mm	DIN 935	1	000000000	0000
				M20 × 2.5 mm	30 mm	22 mm	ISO Class 8	4 mm	DIN 935	1	000000000	0000
				M24 × 3 mm	36 mm	27 mm	ISO Class 8	5 mm	DIN 935	1	000000000	0000
				M30 × 3.5 mm	46 mm	33 mm	ISO Class 8	6.3 mm	DIN 935	1	000000000	00000
				M36 × 3 mm	55 mm	38 mm	ISO Class 8	6.3 mm	DIN 935	1	000000000	00000
M36 × 4 mm				55 mm	38 mm	ISO Class 8	6.3 mm	DIN 935	1	000000000	00000


M42 × 4.5 mm	65 mm			46 mm	ISO Class 8	8 mm	DIN 935	1	000000000	00000
M48 × 5 mm	75 mm			50 mm	ISO Class 8	8 mm	DIN 935	1	000000000	00000
M56 × 5.5 mm	85 mm			57 mm	ISO Class 8	8 mm	DIN 935	1	000000000	00000

Low-Strength Steel

Image of ProductInUse. Front orientation. Locknuts. Locknuts for use with Cotter Pins.

Image of Product. Front orientation. Locknuts. Locknuts for use with Cotter Pins.

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

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.

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

	Wd.	Ht.	For Cotter Pin Dia.	Pkg. Qty.		Pkg.
Zinc-Plated Steel



	1/4"-20	7/16"	7/32"	1/16"	50	000000000	000000


	1/4"-28	7/16"	7/32"	1/16"	50	000000000	00000
	5/16"-18	1/2"	17/64"	5/64"	25	000000000	0000
	5/16"-24	1/2"	17/64"	5/64"	25	000000000	0000
	3/8"-16	9/16"	21/64"	7/64"	25	000000000	00000
	3/8"-24	9/16"	21/64"	7/64"	25	000000000	00000
	7/16"-14	11/16"	3/8"	3/32"	25	000000000	00000
	7/16"-20	11/16"	3/8"	3/32"	25	000000000	00000
	1/2"-13	3/4"	7/16"	1/8"	25	000000000	00000
	1/2"-20	3/4"	7/16"	1/8"	25	000000000	00000
	9/16"-12	7/8"	31/64"	7/64"	10	000000000	00000


	9/16"-18	7/8"	31/64"	7/64"	5	000000000	0000
	5/8"-11	15/16"	35/64"	5/32"	10	000000000	0000
	5/8"-18	15/16"	35/64"	5/32"	10	000000000	0000
	3/4"-10	1 1/8"	21/32"	5/32"	10	000000000	00000
	3/4"-16	1 1/8"	21/32"	5/32"	10	000000000	00000
	7/8"-9	1 5/16"	3/4"	5/32"	5	000000000	00000
	7/8"-14	1 5/16"	3/4"	5/32"	5	000000000	0000
	1"-8	1 1/2"	55/64"	3/16"	5	000000000	00000
	1"-14	1 1/2"	55/64"	3/16"	5	000000000	00000
	1 1/4"-7	1 7/8"	1 3/32"	9/32"	1	000000000	0000


	1 1/4"-12	1 7/8"	1 1/16"	9/32"	1	000000000	0000
	1 1/2"-6	2 1/4"	1 5/16"	5/16"	1	000000000	00000
	1 1/2"-12	2 1/4"	1 5/16"	5/16"	1	000000000	00000
	1 3/4"-5	2 5/8"	1 1/2"	3/8"	1	000000000	00000
	1 3/4"-12	2 5/8"	1 1/2"	3/8"	1	000000000	00000
	2"-4 1/2	3"	1 23/32"	3/8"	1	000000000	00000
	2"-12	3"	1 23/32"	3/8"	1	000000000	00000


	Black-Oxide Steel



			1 1/2"-12	2 1/4"	1 9/32"	5/16"	1	000000000	00000


			Steel



					1/4"-20	7/16"	7/32"	1/16"	25	000000000	0000


					5/16"-24	1/2"	17/64"	5/64"	25	000000000	0000
					1"-14	1 1/2"	55/64"	3/16"	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.

	Wd.	Ht.	For Cotter Pin Dia.	Pkg. Qty.		Pkg.
18-8 Stainless Steel



	10-32	3/8"	1/4"	3/64"	5	000000000	00000


	1/4"-20	7/16"	9/32"	1/16"	5	000000000	0000
	1/4"-28	7/16"	9/32"	1/16"	5	000000000	0000
	5/16"-18	1/2"	21/64"	5/64"	5	000000000	00000
	5/16"-24	1/2"	21/64"	5/64"	5	000000000	00000
	3/8"-16	9/16"	13/32"	3/32"	1	000000000	0000
	3/8"-24	9/16"	13/32"	3/32"	1	000000000	0000
	1/2"-13	3/4"	9/16"	1/8"	1	000000000	0000
	1/2"-20	3/4"	9/16"	1/8"	1	000000000	0000
	5/8"-11	15/16"	23/32"	5/32"	1	000000000	0000
	5/8"-18	15/16"	23/32"	5/32"	1	000000000	0000


	3/4"-10	1 1/8"	13/16"	5/32"	1	000000000	0000
	3/4"-16	1 1/8"	13/16"	5/32"	1	000000000	0000
	7/8"-9	1 5/16"	29/32"	5/32"	1	000000000	00000
	1"-8	1 1/2"	1"	3/16"	1	000000000	00000
	1 1/4"-7	1 7/8"	1 1/4"	7/32"	1	000000000	00000
	1 1/2"-6	2 1/4"	1 1/2"	1/4"	1	000000000	00000

Narrow-Profile Locknuts with External-Tooth Lock Washer

Since they're about 20% narrower, these locknuts fit in tight spaces where standard-profile nuts won't fit. They combine a hex nut with a free-spinning lock washer, so you can twist them into place by hand and save on assembly time. Once the nut is against your material surface, tighten it down with a wrench or socket to get the teeth to bite. Although these nuts install more quickly than nylon-insert locknuts, they don't hold up as well against vibration and can mar your material. As long as the washer stays intact, you can reuse them. Also known as Keps and K-lock nuts.

Low-Strength Steel

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

	Wd.	Ht.	Washer OD	Pkg. Qty.		Pkg.
Zinc-Plated Steel



	6-32	1/4"	1/8"	0.281"	100	000000000	000000


	8-32	5/16"	9/64"	0.344"	100	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.	Washer OD	Pkg. Qty.		Pkg.
18-8 Stainless Steel



	6-32	1/4"	1/8"	0.344"	100	000000000	000000

Assortments of Locknuts with External-Tooth Lock Washer

With a range of sizes on hand, you can use these assortments to fasten a variety of parts. These locknuts combine a hex nut with a free-spinning lock washer, so you can twist them into place by hand and save on assembly time. Once the nut is against your material surface, tighten it down with a wrench or socket to get the teeth to bite. Although these nuts install more quickly than nylon-insert locknuts, they don't hold up as well against vibration and can mar your material. As long as the washer stays intact, you can reuse them. Also known as Keps and K-lock nuts.

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

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.

	Locknuts Included	Container Type		Each
Zinc-Plated Steel



	600	4-40 (100 Pieces) 6-32 (100 Pieces) 8-32 (100 Pieces) 10-24 (100 Pieces) 10-32 (100 Pieces) 1/4"-20 (100 Pieces)	Plastic Box	000000000	000000


	18-8 Stainless Steel



			600	4-40 (100 Pieces) 6-32 (100 Pieces) 8-32 (100 Pieces) 10-24 (100 Pieces) 10-32 (100 Pieces) 1/4"-20 (100 Pieces)	Plastic Box	000000000	00000