Flex-Top Nuts | McMaster-Carr

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Corrosion Resistant

Won't rust in wet and outdoor environments

68 products

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

18 products

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The most common profile of locknut

105 products

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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	94820A370	00000
	1/4"-28	7/16"	5/16"	5	94820A380	0000
	5/16"-18	1/2"	23/64"	5	94820A390	0000
	5/16"-24	1/2"	23/64"	5	94820A410	0000
	3/8"-16	9/16"	15/32"	5	94820A420	0000
	3/8"-24	9/16"	15/32"	5	94820A430	0000
	7/16"-14	5/8"	15/32"	1	94820A440	0000
	1/2"-13	3/4"	39/64"	1	94820A450	0000
	1/2"-20	3/4"	39/64"	1	94820A460	0000
	5/8"-11	15/16"	49/64"	1	94820A470	0000
	5/8"-18	15/16"	49/64"	1	94820A480	0000
	3/4"-10	1 1/16"	57/64"	1	94820A490	0000
	3/4"-16	1 1/16"	57/64"	1	94820A510	0000
	M6 × 1 mm	10 mm	7.8 mm	1	94235A111	0000
	M8 × 1.25 mm	13 mm	10.4 mm	1	94235A112	0000
	M10 × 1.5 mm	15 mm	13 mm	1	94235A113	0000
	M12 × 1.75 mm	19 mm	15.6 mm	1	94235A114	0000

	Cadmium-Plated Steel


			4-40	1/4"	5/32"	10	94820A210	00000
			6-32	5/16"	3/16"	25	94820A215	00000
			8-32	11/32"	1/4"	25	94820A220	00000
			10-24	3/8"	1/4"	25	94820A225	00000
			10-32	3/8"	1/4"	25	94820A230	00000
			1/4"-20	7/16"	19/64"	25	94820A232	00000
			1/4"-28	7/16"	5/16"	25	94820A235	00000
			5/16"-18	1/2"	23/64"	10	94820A237	0000
			5/16"-24	1/2"	23/64"	10	94820A240	0000
			3/8"-16	9/16"	15/32"	10	94820A242	00000
			3/8"-24	9/16"	15/32"	10	94820A245	00000
			7/16"-14	5/8"	15/32"	5	94820A247	00000
			7/16"-20	5/8"	15/32"	1	94820A310	0000
			1/2"-13	3/4"	39/64"	5	94820A249	00000
			1/2"-20	3/4"	39/64"	5	94820A250	00000
			9/16"-18	7/8"	31/64"	1	94820A320	0000
			5/8"-11	15/16"	49/64"	1	94820A252	0000
			5/8"-18	15/16"	49/64"	1	94820A255	0000
			3/4"-10	1 1/16"	57/64"	1	94820A036	0000
			3/4"-16	1 1/16"	57/64"	1	94820A260	0000
			7/8"-9	1 1/4"	1 1/64"	1	94820A330	00000
			7/8"-14	1 1/4"	1 1/64"	1	94820A340	00000
			1"-8	1 7/16"	1 9/64"	1	94820A350	00000
			1"-14	1 7/16"	1 9/64"	1	94820A360	00000
			M6 × 1 mm	10 mm	7.8 mm	5	94235A080	0000
			M8 × 1.25 mm	13 mm	10.4 mm	1	94235A090	0000
			M10 × 1.5 mm	17 mm	13 mm	1	94235A110	0000
			M12 × 1.75 mm	19 mm	15.6 mm	1	94235A120	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.

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


	2-56	1/4"	5/32"	5	91839A105	000000
	6-32	5/16"	3/16"	5	91839A225	0000
	8-32	11/32"	1/4"	5	91839A230	0000
	10-24	3/8"	1/4"	5	91839A235	0000
	10-32	3/8"	1/4"	10	91839A120	00000
	1/4"-20	7/16"	19/64"	5	91839A123	00000
	1/4"-28	7/16"	19/64"	5	91839A125	0000
	5/16"-18	1/2"	23/64"	1	91839A127	0000
	5/16"-24	1/2"	23/64"	1	91839A130	0000
	3/8"-16	9/16"	15/32"	1	91839A132	0000
	3/8"-24	9/16"	15/32"	1	91839A135	0000
	7/16"-20	5/8"	15/32"	1	91839A140	00000
	1/2"-13	3/4"	39/64"	1	91839A033	0000
	1/2"-20	3/4"	39/64"	1	91839A145	0000
	M3 × 0.5 mm	5.5 mm	4.5 mm	1	94560A111	0000
	M4 × 0.7 mm	7 mm	6 mm	1	94560A112	0000
	M5 × 0.8 mm	8 mm	7.5 mm	1	94560A113	0000
	M6 × 1 mm	10 mm	7.8 mm	1	94560A060	0000
	M8 × 1.25 mm	13 mm	10.4 mm	1	94560A080	0000
	M10 × 1.5 mm	17 mm	13 mm	1	94560A100	00000
	M12 × 1.75 mm	19 mm	15.6 mm	1	94560A120	00000
	M14 × 2 mm	22 mm	18.2 mm	1	94560A114	00000
	M16 × 2 mm	24 mm	20.8 mm	1	94560A115	00000
	M18 × 2.5 mm	27 mm	23.4 mm	1	94560A116	00000
	M20 × 2.5 mm	30 mm	26 mm	1	94560A117	00000
	M22 × 2.5 mm	32 mm	28.6 mm	1	94560A118	00000
	M24 × 3 mm	36 mm	31.2 mm	1	94560A119	00000

	Black-Oxide 18-8 Stainless Steel


			8-32	11/32"	1/4"	5	91839A311	0000
			10-24	3/8"	1/4"	5	91839A312	0000
			10-32	3/8"	1/4"	5	91839A313	0000
			1/4"-20	7/16"	19/64"	5	91839A314	00000
			3/8"-16	9/16"	15/32"	1	91839A316	0000
			1/2"-13	3/4"	39/64"	1	91839A317	0000
			1/2"-20	3/4"	39/64"	1	91839A318	0000

			316 Stainless Steel


					M3 × 0.5 mm	5.5 mm	4.5 mm	1	94560A110	0000
					M4 × 0.7 mm	7 mm	6 mm	1	94560A130	0000
					M5 × 0.8 mm	8 mm	7.5 mm	1	94560A140	0000
					M6 × 1 mm	10 mm	7.8 mm	1	94560A150	0000
					M8 × 1.25 mm	13 mm	10.4 mm	1	94560A160	00000
					M10 × 1.5 mm	17 mm	13 mm	1	94560A170	00000
					M12 × 1.75 mm	19 mm	15.6 mm	1	94560A180	00000
					M20 × 2.5 mm	30 mm	26 mm	1	94560A190	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	94830A485	000000
	8-32	11/32"	3/16"	25	94830A490	00000
	10-24	3/8"	3/16"	25	94830A495	00000
	10-32	3/8"	3/16"	25	94830A505	00000
	1/4"-20	7/16"	7/32"	25	94830A510	00000
	1/4"-28	7/16"	7/32"	25	94830A515	00000
	5/16"-18	1/2"	17/64"	10	94830A520	0000
	5/16"-24	1/2"	17/64"	10	94830A525	0000
	3/8"-16	9/16"	9/32"	10	94830A530	00000
	3/8"-24	9/16"	9/32"	10	94830A535	00000
	7/16"-20	5/8"	21/64"	5	94830A540	0000
	1/2"-13	3/4"	21/64"	5	94830A545	0000
	1/2"-20	3/4"	21/64"	5	94830A550	0000
	5/8"-11	15/16"	13/32"	1	94830A560	0000
	5/8"-18	15/16"	13/32"	1	94830A565	0000
	3/4"-10	1 1/16"	27/64"	1	94830A570	0000
	3/4"-16	1 1/16"	27/64"	1	94830A436	0000
	7/8"-9	1 1/4"	31/64"	1	94830A120	00000
	1"-8	1 7/16"	37/64"	1	94830A038	0000
	1"-14	1 7/16"	37/64"	1	94830A438	0000
	1 1/4"-12	1 13/16"	49/64"	1	94830A122	00000
	1 1/2"-12	2 3/16"	57/64"	1	94830A123	00000

	Steel


			6-32	5/16"	9/64"	10	94830A124	0000
			8-32	11/32"	3/16"	10	94830A125	0000
			10-24	3/8"	3/16"	10	94830A126	0000
			10-32	3/8"	3/16"	10	94830A127	0000
			1/4"-20	7/16"	7/32"	10	94830A128	0000
			1/4"-28	7/16"	7/32"	10	94830A129	0000
			5/16"-18	1/2"	17/64"	5	94830A130	0000
			5/16"-24	1/2"	17/64"	5	94830A131	0000
			3/8"-16	9/16"	9/32"	5	94830A132	0000
			3/8"-24	9/16"	9/32"	5	94830A133	0000
			1/2"-13	3/4"	21/64"	1	94830A134	0000
			1/2"-20	3/4"	21/64"	1	94830A135	0000
			5/8"-11	15/16"	13/32"	1	94830A136	0000
			5/8"-18	15/16"	13/32"	1	94830A137	0000
			3/4"-10	1 1/16"	27/64"	1	94830A138	0000
			3/4"-16	1 1/16"	27/64"	1	94830A139	0000
			1"-14	1 7/16"	37/64"	1	94830A140	0000
			1 1/8"-12	1 5/8"	41/64"	1	94830A141	00000
			1 1/4"-12	1 13/16"	49/64"	1	94830A142	00000
			1 3/8"-12	1 15/16"	53/64"	1	94830A143	00000
			1 1/2"-12	2 3/16"	57/64"	1	94830A144	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	94140A100	000000
	8-32	11/32"	3/16"	5	94140A103	00000
	10-24	3/8"	3/16"	5	94140A105	00000
	10-32	3/8"	3/16"	10	94140A107	00000
	1/4"-20	7/16"	7/32"	5	94140A131	00000
	1/4"-28	7/16"	7/32"	5	94140A109	00000
	5/16"-18	1/2"	17/64"	1	94140A139	0000
	5/16"-24	1/2"	17/64"	1	94140A143	0000
	3/8"-16	9/16"	9/32"	1	94140A147	0000
	3/8"-24	9/16"	9/32"	1	94140A151	0000
	1/2"-13	3/4"	21/64"	1	94140A155	0000
	1/2"-20	3/4"	21/64"	1	94140A159	00000
	5/8"-18	15/16"	13/32"	1	94140A162	00000
	3/4"-16	1 1/16"	27/64"	1	94140A163	00000
	7/8"-14	1 1/4"	31/64"	1	94140A164	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	94827A110	000000
	5/16"-18	9/16"	21/64"	10	94827A120	00000
	3/8"-16	5/8"	25/64"	10	94827A130	00000
	1/2"-13	13/16"	1/2"	5	94827A150	00000
	5/8"-11	1"	41/64"	1	94827A160	0000
	3/4"-10	1 1/8"	49/64"	1	94827A036	0000
	7/8"-9	1 5/16"	57/64"	1	94827A037	00000
	1"-8	1 1/2"	1 1/64"	1	94827A038	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	95070A210	000000
	5/16"-18	9/16"	21/64"	1	95070A310	00000
	3/8"-16	5/8"	25/64"	1	95070A410	00000
	7/16"-14	3/4"	29/64"	1	95070A510	00000
	1/2"-13	13/16"	1/2"	1	95070A610	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	94828A410	000000
	5/16"-18	9/16"	17/64"	10	94828A420	0000
	3/8"-16	5/8"	9/32"	10	94828A425	00000
	7/16"-14	3/4"	21/64"	1	94828A430	0000
	1/2"-13	13/16"	21/64"	5	94828A435	00000
	5/8"-11	1"	13/32"	1	94828A440	0000
	3/4"-10	1 1/8"	27/64"	1	94828A036	00000
	7/8"-9	1 5/16"	31/64"	1	94828A037	00000
	1"-8	1 1/2"	37/64"	1	94828A038	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	99638A101	000000
	6-32	5/16"	3/16"	MS21045-06	5	99638A102	0000
	8-32	11/32"	1/4"	MS21045-08	5	99638A103	00000
	10-32	3/8"	1/4"	MS21045-3	5	99638A100	0000
	1/4"-28	7/16"	5/16"	MS21045-4	5	99638A200	00000
	5/16"-24	1/2"	23/64"	MS21045-5	5	99638A300	00000
	3/8"-24	9/16"	15/32"	MS21045-6	5	99638A400	00000
	7/16"-20	11/16"	15/32"	MS21045-7	1	99638A500	00000
	1/2"-20	3/4"	39/64"	MS21045-8	1	99638A600	00000
	9/16"-18	7/8"	11/16"	MS21045-9	1	99638A700	00000
	5/8"-18	15/16"	49/64"	MS21045-10	1	99638A800	00000
	3/4"-16	1 1/16"	57/64"	MS21045-12	1	99638A900	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	99851A101	000000
	6-32	5/16"	11/64"	MS21046C06	NASM21046	1	99851A102	00000
	8-32	11/32"	15/64"	MS21046C08	NASM21046	1	99851A103	0000
	10-32	3/8"	15/64"	MS21046C3	NASM21046	1	99851A104	00000
	1/4"-28	7/16"	9/32"	MS21046C4	NASM21046	1	99851A105	00000
	3/8"-24	9/16"	25/64"	MS21046C6	NASM21046	1	99851A106	00000