What Are Those Small Metal Balls Called? Names & Uses Explained

What Are Those Small Metal Balls Actually Called?

The most common answer is ball bearings — but that's only part of the story. Small metal balls go by several different names depending on their function, material, and industry. The term "ball bearing" refers specifically to the precision-ground spheres used inside bearing assemblies to reduce friction between rotating parts. However, small metal balls also appear as steel balls, metal shot, pellets, BBs, grinder media, and decorative spheres, each with its own technical definition and application.

If you've seen small metal balls inside a machine, a piece of jewelry, a toy gun, or a paint can, they likely have different names. This article breaks down every major category of small metal balls, what they're called, what they're made from, and where they're actually used — with real measurements and examples throughout.

Ball Bearings: The Most Recognized Small Metal Balls

Ball bearings are precision-engineered spheres that sit inside a ring-shaped housing called a race. Their job is to transfer load and minimize friction between a rotating shaft and a fixed structure. Without them, motors, wheels, and turbines would grind themselves apart within minutes.

The balls themselves are manufactured to extremely tight tolerances. According to the ABMA (American Bearing Manufacturers Association), Grade 25 bearing balls — among the highest quality commonly used — must have a diameter deviation of no more than 0.000025 inches (0.635 micrometers). That's smaller than a red blood cell.

Common sizes range from 1 mm to 50 mm in diameter, though specialty applications use balls outside this range. For example, miniature bearings in dental drills use balls as small as 0.5 mm, while large industrial gearboxes may use balls exceeding 75 mm.

Materials Used in Ball Bearings

• Chrome steel (52100 alloy) — the most common material, offering excellent hardness and fatigue resistance
• Stainless steel (AISI 440C) — used in food processing, medical equipment, and marine environments where corrosion is a concern
• Ceramic (silicon nitride) — used in high-speed, high-temperature applications; 60% lighter than steel with superior hardness
• Carbon steel — a lower-cost option for non-critical applications
• Tungsten carbide — extreme hardness for abrasive environments like mining equipment

Ball bearings appear in almost every mechanical device you've ever used: bicycles, electric motors, hard drives, skateboards, washing machines, aircraft engines, and industrial conveyor systems. The global ball bearing market was valued at approximately $14.5 billion in 2023, which reflects just how pervasive these small metal balls are in modern manufacturing.

Steel Balls: A Broader Category Than Ball Bearings

The term steel balls is more general than ball bearings. It refers to any spherical object made from steel, regardless of its intended use. Ball bearings are a type of steel ball, but not all steel balls are ball bearings.

Steel balls are used across dozens of industries. In the mining and cement industries, for example, large steel balls ranging from 20 mm to 150 mm are loaded into rotating drum mills to grind ore and clinker into powder. These are called grinding balls or milling balls, and a single cement plant may consume hundreds of tons of them per year.

Smaller steel balls are used as check valves in hydraulic systems, as agitation media inside aerosol paint cans (you hear them rattling when you shake the can), and as the rolling element inside ballpoint pens. The ball in a standard ballpoint pen is typically 0.7 mm or 1.0 mm in diameter and is often made from brass or tungsten carbide rather than standard steel.

BBs and Pellets: Small Metal Balls in Shooting Sports

In the context of air guns and shooting, small metal balls are almost universally called BBs. The term originally referred to a specific size of lead shot used in shotgun shells — "BB" was simply a size designation in the standard shot-size chart. Over time, it became associated with the small round projectiles fired by air guns.

Modern BBs are typically made from steel and coated with copper or zinc to resist corrosion. The standard BB diameter is 4.5 mm (0.177 inches). They weigh approximately 0.35 grams each. Lead BBs and balls are still used in some traditional contexts, particularly in muzzleloaders and antique firearms.

The distinction between BBs and pellets is worth clarifying. Pellets are not spherical — they have a waisted diabolo shape — while BBs are true round metal balls. In competitive 10-meter air pistol shooting, athletes use 4.5 mm lead pellets, not BBs, because pellets are more accurate over distance.

Airsoft BBs, used in recreational shooting sports, are usually 6 mm in diameter and made from ABS plastic rather than metal, though metal airsoft BBs do exist and are used in specific scenarios requiring greater mass and velocity.

Steel Shot and Metal Shot: Industrial and Surface Treatment Applications

Steel shot refers to small spherical metal balls used in surface preparation processes. They are blasted at high velocity against metal surfaces to clean rust, mill scale, and old coatings — a process called shot blasting. The same balls, when used to deliberately compress the surface layer of a metal part to improve fatigue strength, participate in a process called shot peening.

Shot sizes are defined by standardized codes. For example, S-110 shot has a nominal diameter of 0.30 mm, while S-780 shot has a nominal diameter of 2.0 mm. The choice of shot size depends on the surface finish required and the hardness of the workpiece.

Shot peening is critical in aerospace manufacturing. Turbine blades, landing gear components, and structural airframe parts are routinely peened to extend their service life. Studies have shown that shot peening can increase the fatigue life of certain steel components by up to 1000% under cyclic loading conditions.

Metal shot is also used in die casting as a cleaning medium, in the foundry industry to clean castings, and in the preparation of steel structures before painting or powder coating.

Marbles: When Metal Balls Meet Play and Decoration

While traditional marbles are made from glass, steel marbles are a real and popular variation. They're commonly called steelies in playground culture, and they've been used competitively in marble games for generations because their weight gives them greater striking power against glass marbles.

Steel marbles are typically 12.7 mm to 25.4 mm (½ inch to 1 inch) in diameter and are essentially repurposed or surplus ball bearing balls. They are sold in toy stores and online in bulk bags and are also used in science experiments, executive desk toys, and as weights in craft projects.

Decorative metal balls — often made from stainless steel, brass, or copper — are used in garden ornaments, architectural features, and interior design. Large polished stainless steel spheres, sometimes called gazing balls or garden balls, can measure anywhere from 100 mm to over 600 mm in diameter and serve purely aesthetic purposes.

A Comparison of Small Metal Ball Types by Name, Size, and Use

How Small Metal Balls Are Manufactured

The manufacturing process for precision metal balls is more involved than most people realize. For ball bearings and high-precision steel balls, the process typically follows these stages:

1. Wire drawing — steel wire is drawn to a specific diameter
2. Cold heading — the wire is cut and pressed into a rough sphere using a cold heading machine; this leaves a visible ring called a "flash" or "parting line"
3. Flash removal — the parting line is removed by rolling the balls between hardened steel plates
4. Heat treatment — balls are hardened and tempered to achieve the required surface hardness, typically 58–66 HRC (Rockwell C hardness)
5. Hard grinding — balls are ground to near-final size using abrasive wheels
6. Lapping — final polishing using fine abrasive compounds brings the balls to their specified diameter and surface finish
7. Inspection and sorting — each ball is measured and sorted by grade

The surface finish of a Grade 25 bearing ball must have a roughness value (Ra) of no more than 0.012 micrometers — smoother than most polished mirrors. Achieving this requires multiple lapping passes with progressively finer abrasive compounds.

Less precise metal balls — such as grinding balls or steel shot — are manufactured by simpler methods. Grinding balls are usually made by hot rolling or casting, while steel shot is produced by atomizing molten steel: a stream of liquid metal is blasted with high-pressure water or air, causing it to break into droplets that solidify into spherical particles as they cool.

Metal Balls in Everyday Objects You Might Not Have Noticed

Small metal balls appear in far more everyday objects than most people ever think about. Here are some specific examples:

• Ballpoint pens — the writing tip contains a single metal ball, usually 0.7 mm or 1.0 mm in diameter, that rolls against the ink reservoir to deposit ink on paper. Most are made from brass or tungsten carbide.
• Aerosol paint cans — a steel ball is placed inside the can to help mix the propellant and pigment when you shake the can. Without it, the paint would settle and spray unevenly.
• Roll-on deodorant bottles — these use a large plastic or sometimes metal ball to transfer product from the reservoir to skin. The concept is directly borrowed from the ballpoint pen.
• Skateboard wheels — the axle passes through a bearing assembly packed with precision steel balls, typically 7 or 8 balls per bearing in a standard ABEC-rated skateboard bearing.
• Computer hard disk drives — older spinning-platter HDDs used ball bearings in the spindle motor. Many modern drives have switched to fluid dynamic bearings for quieter operation, but ball bearings remain in millions of devices still in use.
• Fidget spinners — the central bearing that allows a fidget spinner to rotate contains a ring of small steel balls, typically 6 or 7 balls of about 3 mm diameter.
• Car wheel hubs — tapered roller bearings or ball bearings in car wheel assemblies allow the wheel to rotate with minimal friction while bearing the full weight of the vehicle.
• Kitchen appliances — stand mixers, food processors, and blenders contain ball bearings in their motor shafts to handle both radial and axial loads during operation.

Specialty and Exotic Metal Balls: Beyond Steel

While steel dominates, small metal balls are also manufactured from a wide range of other materials for specific applications:

Tungsten Carbide Balls

Tungsten carbide is one of the hardest materials on earth, with a Vickers hardness of around 1500–1800 HV compared to around 800 HV for hardened bearing steel. Tungsten carbide balls are used in ballpoint pens (because they resist wear from rough paper), in flow meters, and in applications involving highly abrasive fluids. They are significantly heavier than steel — tungsten carbide has a density of approximately 15.6 g/cm³ versus 7.8 g/cm³ for steel.

Brass and Copper Balls

Brass balls are softer and more corrosion-resistant than steel, making them suitable for use in valves, plumbing fittings, and artistic applications. Copper balls are used in electrical grounding applications and in some laboratory equipment. Their warm color also makes them popular in decorative metalwork and jewelry-making contexts.

Titanium Balls

Titanium balls offer an exceptional strength-to-weight ratio and outstanding corrosion resistance, including resistance to seawater and many aggressive chemicals. They are used in aerospace hydraulic systems, in medical implants, and in the chemical processing industry. Titanium's density is only 4.5 g/cm³ — about 58% lighter than steel for the same volume — which matters enormously in weight-sensitive aerospace applications.

Aluminum Balls

Aluminum balls are lightweight and non-magnetic, making them useful in certain scientific instruments, decorative applications, and environments where magnetic interference must be avoided. They are also used in some grounding applications in the electrical industry and as lightweight ballast in various engineering projects.

Gold, Silver, and Precious Metal Balls

In jewelry making, small gold and silver balls are called bead balls or granules. Granulation is an ancient goldsmithing technique dating back over 5,000 years, in which tiny spheres of gold are fused to a base without visible solder. Some Etruscan jewelry pieces feature granules as small as 0.14 mm in diameter, a feat of craftsmanship that modern artisans still struggle to replicate.

How to Identify What Kind of Small Metal Ball You're Looking At

If you've found a small metal ball and want to figure out what it is, consider these identifying factors:

• Size — measure the diameter. Under 5 mm typically points to a bearing ball or BB. 5–15 mm might be a marble or bearing. 20 mm and above points to a grinding ball or decorative sphere.
• Surface finish — ball bearings are mirror-polished with no visible seams. Shot and grinding balls are rougher. BBs have a visible coating.
• Magnetism — most steel balls are strongly magnetic. Stainless steel (304 grade) is weakly magnetic or non-magnetic. Titanium, brass, copper, and aluminum are non-magnetic.
• Weight — tungsten carbide and steel are heavy. Aluminum and titanium feel noticeably lighter for the same size.
• Color — silver-gray is typical for steel; gold-toned for brass; reddish for copper; slightly darker gray for tungsten carbide.
• Context — where did you find it? Inside a machine = likely a bearing ball. In a bag with a paint can = agitator ball. On a shooting range = BB or steel shot.

Why the Precision of Metal Balls Matters More Than You'd Think

The roundness of a ball bearing — how close it is to a perfect sphere — directly affects the performance and lifespan of the machine it's used in. A ball that deviates from a perfect sphere by even a few micrometers will create vibration, uneven load distribution, and premature wear in the bearing housing.

This is why precision ball grades are so carefully defined. ABMA Grade 3 balls, the most precise commercially available, have a sphericity deviation of no more than 0.08 micrometers — that's 0.08 millionths of a meter. By comparison, a human hair is approximately 70,000 micrometers wide. Achieving this level of precision requires state-of-the-art lapping machines, ultra-clean manufacturing environments, and meticulous quality inspection using laser measurement systems.

In the semiconductor industry, bearings supporting wafer-handling robots must operate at high speeds with essentially zero vibration to avoid damaging circuits measured in nanometers. A single vibration event caused by an imprecise bearing ball could destroy an entire batch of wafers worth hundreds of thousands of dollars. This is why precision metal balls — despite being small, simple objects — remain the subject of continuous engineering research and refinement.