4mm Balls | McMaster-Carr

The best choice for high-performance bearings and valves, these 440C stainless steel balls are among the strongest, hardest, and most wear-resistant we offer. They’re passivated to wash away surface particles that cause rust, and they’re polished to a mirror-like finish that contaminants can’t stick to. The result is balls that stay smooth and stand the test of time—even at temperatures up to 800° F. They’re made to strict ISO 3290 standards for roundness and surface quality.

These balls are magnetic, so you can use them in separators, sensors, and automated handling systems that use magnetic pickup or positioning.

Grade 25—Precision-ground to tighter tolerances than Grade 100 balls. Use them in high-accuracy assemblies.

Certificates with a traceable lot number are available for these products. Download certificates from ORDER HISTORY after your order ships.

							Stainless Steel Balls
	Dia., mm	Dia. Tolerance, mm	Hardness	Specs. Met	Magnetic Properties	Appearance	Pkg. Qty.		Pkg.
Grade 25



		4	-0.0025 to 0.0025	Rockwell C58 (Extra Hard)	ISO 3290	Magnetic	Mirror Like	50	1598K25	00000

Multipurpose 304 Stainless Steel Balls

Whether inside pumps or furnace parts, these balls can be used in any mildly corrosive, high-temperature conditions. Made of 304 stainless steel, they won’t degrade when exposed to mild chemicals and water, even at temperatures up to 1500° F. They’re passivated to wash away surface particles that cause rust, and they’re polished to a mirror-like finish that contaminants can’t stick to. The result is balls that stay smooth and stand the test of time. These balls are made to strict ISO 3290 standards for roundness and surface quality.

Although 304 balls aren’t as wear resistant as 440C balls, they’re easier to fabricate. They’re also nonmagnetic.

Grade 100—Great for mechanical applications where you don’t need the exacting tolerances of Grade 25.

Certificates with a traceable lot number are available for these products. Download certificates from ORDER HISTORY after your order ships.

								Stainless Steel Balls
	Dia., mm	Dia. Tolerance, mm	Fabrication	Hardness	Specs. Met	Magnetic Properties	Appearance	Pkg. Qty.		Pkg.
Grade 100



		4	-0.0127 to 0.0127	Cold Worked	Rockwell C25 (Hard)	ASTM A240, ISO 3290, SAE J405	Nonmagnetic	Mirror Like	50	9291K75	00000

Steel Balls

Multipurpose Low-Carbon Steel—Low-carbon steel balls are our easiest steel balls to machine. They are often used for parts that don’t require high strength, such as knobs. These balls can be surface hardened with heat treating for added wear resistance.

Wear-Resistant 52100 Alloy Steel—High carbon and chromium content makes this 52100 alloy steel extremely hard and resistant to wear. It’s also known as chrome steel. Often used as bearings, these balls are hardened for increased abrasion and impact resistance.

	Dia. Tolerance, mm	Heat Treatment	Yield Strength, psi	Mechanical Finish	Hardness	Appearance	Pkg. Qty.		Pkg.
Multipurpose Low-Carbon Steel



	4	-0.13 to 0.13	Case Hardened	44,000	Tumbled	Rockwell C60 (Extra Hard)	Mirror Like	1,000	96455K128	000000


	Wear-Resistant 52100 Alloy Steel



			4	-0.0025 to 0.0025	Hardened	295,000	—	Rockwell C60 (Extra Hard)	Mirror Like	100	9292K37	0000

Highly Corrosion-Resistant 316 Stainless Steel Balls

Trusted in marine and chemical-processing valves, these balls stand up to some of the most highly corrosive environments. Made of 316 stainless steel, they hold up to sulfuric acid, chlorine, and other harsh chemicals in temperatures as high as 1500° F. They’re a step up from balls made of 304, which have similar strength and temperature performance. They’re passivated to wash away surface particles that cause rust, and they’re polished to a mirror-like finish that contaminants can’t stick to. The result is balls that stay smooth and stand the test of time. They’re made to strict ISO 3290 standards for roundness and surface quality.

Although 316 balls aren’t as wear resistant as 440C balls, they’re easier to fabricate. They’re also nonmagnetic.

Grade 100—Great for mechanical applications where you don’t need the exacting tolerances of Grade 25.

Certificates with a traceable lot number are available for these products. Download certificates from ORDER HISTORY after your order ships.

								Stainless Steel Balls
	Dia., mm	Dia. Tolerance, mm	Mechanical Finish	Hardness	Specs. Met	Magnetic Properties	Appearance	Pkg. Qty.		Pkg.
Grade 100



		4	-0.013 to 0.013	Tumbled	Rockwell C25 (Hard)	ISO 3290	Nonmagnetic	Mirror Like	50	96415K57	00000

Plastic Balls

Delrin® Acetal—Able to hold tight tolerances, these balls resist expanding when exposed to heat and moisture. They have a naturally slippery, wear-resistant surface. Use them for bearings and low-load rolling applications. Delrin® acetal resin is also known as acetal homopolymer.

	Max. Temp., ° F	Tensile Strength, psi	Impact Strength, ft·lbf/in	Color	Food Industry Std.	Pkg. Qty.		Pkg.
Multipurpose







	Delrin® Acetal

	4	-0.0254 to 0.0254	-20	180	10,000 to 11,000	1 to 1.5	White	FDA Standard	100	9614K73	00000

Extra-Hard C2 Tungsten Carbide

Machine long-lasting tools, such as end mills and inserts, with these rods. Tungsten carbide, sometimes called carbide, is harder than our Corrosion-Resistant Tungsten with excellent wear resistance. Its extreme hardness lets cutting edges stay sharp far longer than high-speed steel.

Balls

Dia. Tolerance, mm	Mechanical Finish	Yield Strength	Hardness	Temper Rating	Pkg. Qty.		Pkg.



4	-0.0025 to 0.0025	Polished	Not Rated	Rockwell C75 (Extra Hard)	Not Rated	2	9686K85	000000

High-Strength Fracture- and Wear-Resistant Zirconia Ceramic Balls

Often used instead of metal in bearings and rollers, these balls are ideal for applications where strength under heavy loads and wear resistance is needed. It's the addition of yttria that gives this zirconia more strength and lowers the chances of cracking from impact than standard zirconia, alumina, and silicon nitride ceramic. If cracks do occur, they will not spread, extending the life and reliability of the material. It also means this zirconia blend resists wearing down from rubbing against another part or abrasion from chemical slurries.

These balls do not withstand rapid temperature changes or high temperatures as well as other high-performance ceramics such as ceramic alumina and silicon nitride ceramic.

			Temp., ° F
Dia., mm	Dia. Tolerance, mm	Color	Min.	Max.	Fabrication	Performance	Dielectric Strength, V/mil	Porosity	Compressive Strength, psi	Hardness	Pkg. Qty.		Pkg.



	4	-0.0001 to 0.0001	White	-112	2,700	Sintered	Fracture Resistant, High Strength, Wear Resistant	220	13%	350,000	Rockwell 45N 81	5	5917N19	000000

Nonporous Ceramic Alumina Balls

Seal out air and gas in high-temperature and high-wear applications. This ultrahard ceramic can also be used in applications that require superior strength.

				Temp.
Dia., mm	Dia. Tolerance	Sphericity Percentage	Color	Min.	Max., ° F	Fabrication	Dielectric Strength, V/mil	Porosity	Compressive Strength, psi	Hardness		Each



	4	-0.0001" to 0.0001"	99.99%	White	Not Rated	2,000	Fired	220	Not Rated	300,000	Rockwell 45N 83	9599K35	00000

Tumbling Media for Steel, Stainless Steel, and Hard Metals

Ball

Made of a hard material, this tumbling media is tough enough to finish steel, stainless steel, and other hard metal parts. Choose the shape that best matches the contours of your part and a size that’s large enough not to get stuck in recesses and holes. You can also mix shapes and sizes to tailor the finish to your part.

For Mirror Finish—Use this media as the final step in your finishing process to create a reflective finish. Ideal for fragile parts, it rubs the surface without removing material.

Ball—Best for gentle finishing. Balls are less aggressive than other shapes, so they smooth your workpiece without flattening any details.

Wet Tumbling Condition—Use this media with liquid cleaners.

							5 lb.
	Dia., mm	Density, lb/ft³	Recommended Media to Parts Ratio	Abrasion Type	Tumbling Condition	Material		Pkg.
For Mirror Finish







				Ball

				4	125	3:1	None	Wet	Porcelain	4334A34	000000