9/16"-12 Locknuts | McMaster-Carr

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Zinc Yellow-Chromate Plated

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20 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

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-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.

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



	9/16"-12	7/8"	41/64"	SAE Grade 8	185	5	97135A260	00000


	Black-Oxide Steel



			9/16"-12	7/8"	41/64"	SAE Grade 8	185	5	97135A425	0000


			Steel



					9/16"-12	7/8"	41/64"	SAE Grade 8	185	5	90630A201	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.	Ht.	Fastener Strength Grade/Class	Insert Max. Temp., ° F	Pkg. Qty.		Pkg.
Zinc-Plated Steel



	9/16"-12	7/8"	41/64"	SAE Grade 5	185	25	95615A230	000000


	Black-Oxide Steel



			9/16"-12	7/8"	41/64"	SAE Grade 5	185	25	95615A116	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.	Ht.	Insert Max. Temp., ° F	Pkg. Qty.		Pkg.
Zinc-Plated Steel



	9/16"-12	7/8"	41/64"	185	25	90640A134	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.

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.	Ht.	Insert Max. Temp., ° F	Pkg. Qty.		Pkg.
18-8 Stainless Steel



	9/16"-12	7/8"	41/64"	185	1	91831A034	00000


	316 Stainless Steel



			9/16"-12	7/8"	41/64"	185	1	90715A173	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.

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.

				Flange
	Thread Size	Wd.	Ht.	Dia.	Thk.	Fastener Strength Grade/Class	Pkg. Qty.		Pkg.
Zinc-Yellow-Chromate-Plated Steel



		9/16"-12	7/8"	1/2"	1 3/16"	0.05"	SAE Grade 8	5	95922A114	000000

Low-Strength Steel

About half the strength of medium-strength steel nuts, these 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-Oxide Steel—Typically chosen for their appearance, these nuts have a dark, matte coating that creates a finished look. They offer minimal corrosion resistance, so they're best for dry environments.

				Flange
	Thread Size	Wd.	Ht.	Dia.	Thk.	Pkg. Qty.		Pkg.
Zinc-Plated Steel



		9/16"-12	7/8"	1/2"	1 3/16"	0.05"	10	94831A680	000000


		Black-Oxide Steel



				9/16"-12	7/8"	1/2"	1 3/16"	0.05"	1	93083A119	0000

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.

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.

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

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



	9/16"-12	7/8"	31/64"	ASTM Grade C	10	99291A160	00000


	Zinc-Plated Steel



			9/16"-12	7/8"	31/64"	ASTM Grade C	25	92501A531	00000


			Black-Oxide Steel



					9/16"-12	7/8"	31/64"	ASTM Grade C	10	99291A380	00000


					Cadmium-Plated Steel



							9/16"-12	7/8"	31/64"	ASTM Grade C	25	92501A442	00000


							Steel



									9/16"-12	7/8"	31/64"	ASTM Grade C	25	92501A511	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.	Ht.	Insert Max. Temp., ° F	Pkg. Qty.		Pkg.
Zinc-Plated Steel



	9/16"-12	7/8"	23/64"	220	100	90566A231	000000

Center-Lock Distorted-Thread Locknuts

Also known as reversible locknuts, these thread on from either side, so you don't have to worry about fastening them incorrectly and damaging your screw. The irregularly shaped threads in the middle 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

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



	9/16"-12	7/8"	31/64"	SAE Grade 8	10	90636A066	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.

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



	9/16"-12	7/8"	31/64"	SAE Grade 5	9/64"	10	97190A150	000000

Low-Strength Steel

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

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



	9/16"-12	7/8"	31/64"	7/64"	10	95030A220	000000