When it comes to machining, milling, drilling, and other precision tool operations, one small but powerful component plays a critical role: the collet.
A collet is a sleeve or holding device that grips a tool (like a drill bit, end mill, or tap) with high precision. By securing the tool inside a machine spindle, the collet ensures accuracy, stability, and safety during machining operations.
But here’s the tricky part—collets come in different sizes and systems. If you choose the wrong one, you risk damaging the tool, the machine, or the workpiece. That’s why having a collet size chart is essential for machinists, engineers, and hobbyists.
In this complete guide, we’ll cover:
What a collet is and why it’s important
Different types of collets
A complete collet size chart (ER collets, R8 collets, 5C collets, and more)
Common uses for different collet sizes
Tips for choosing the right collet
Maintenance and care advice
What is a Collet?
A collet is a cylindrical sleeve designed to form a collar around a tool or workpiece. When tightened inside a machine spindle, the collet clamps evenly around the tool, holding it securely in place.
Key benefits of collets include:
High precision (less runout than a regular chuck)
Strong grip (more surface contact with the tool)
Vibration reduction (improves machining quality)
Versatility (compatible with drills, end mills, taps, and reamers)
Collets are widely used in CNC machining, milling, drilling, turning, and woodworking.
Types of Collets
There are many types of collets, but the most commonly used include:
ER Collets
The most popular system in CNC machining.
Available in different series: ER11, ER16, ER20, ER25, ER32, ER40, etc.
Wide clamping range and high accuracy.
R8 Collets
Common in milling machines, especially Bridgeport-style mills.
Designed for quick tool changes.
5C Collets
Used mostly for workholding rather than toolholding.
Popular in lathes and grinders.
Other Collets
TG collets: Similar to ER but with stronger clamping force.
DA collets: Lighter clamping force, used in lighter machining.
Morse Taper (MT) collets: Used in older-style drill presses.
ER Collet Sizes Chart
The ER collet system is the most versatile and widely used worldwide. Each ER series collet can clamp a range of tool shank diameters.
| ER Series | Clamping Range (mm) | Common Uses |
|---|---|---|
| ER8 | 0.5 – 5 mm | Small drills, engraving tools |
| ER11 | 1 – 7 mm | PCB drills, light machining |
| ER16 | 1 – 10 mm | Small milling, light cutting |
| ER20 | 1 – 13 mm | General-purpose milling, tapping |
| ER25 | 1.5 – 16 mm | CNC milling, reaming |
| ER32 | 2 – 20 mm | Heavy milling, drilling |
| ER40 | 3 – 26 mm | Large end mills, heavy-duty tools |
| ER50 | 6 – 34 mm | Heavy machining, industrial use |
R8 Collet Sizes Chart
R8 collets are mainly used in milling machines to hold tools like end mills and drills.
| R8 Collet Size | Tool Diameter (inch) | Common Uses |
|---|---|---|
| 1/8″ | 0.125″ | Small end mills, engraving |
| 3/16″ | 0.1875″ | Small drills |
| 1/4″ | 0.25″ | General small tools |
| 3/8″ | 0.375″ | End mills |
| 1/2″ | 0.50″ | Standard milling cutters |
| 5/8″ | 0.625″ | Larger drills |
| 3/4″ | 0.75″ | Large end mills |
| 7/8″ | 0.875″ | Heavy tools |
| 1″ | 1.00″ | Industrial milling |
5C Collet Sizes Chart
The 5C collet is mainly used for holding round, hex, or square stock in lathes and grinders.
| Collet Type | Size Range | Common Uses |
|---|---|---|
| Round 5C | 1/16″ to 1-1/8″ | Round bars, rods |
| Hex 5C | 1/16″ to 7/8″ | Hexagonal stock |
| Square 5C | 1/16″ to 3/4″ | Square stock |
| Emergency 5C | Custom bored | Unique shapes and custom workpieces |
Common Collet Sizes and Applications
Not every collet size is used daily. The most common ones include:
ER16 and ER20: Standard for small to medium CNC machines.
ER32: The most popular size for milling and drilling.
ER40: Heavy-duty machining requiring larger tool shanks.
R8 1/2″ and 3/4″: Widely used in Bridgeport milling machines.
5C 1/2″ and 3/4″: Common for holding round bar stock in lathes.
Tips for Choosing the Right Collet
Match the collet to the machine spindle – Check if your CNC or mill supports ER, R8, or 5C.
Select the correct size range – Choose a collet that matches your tool diameter.
Consider runout accuracy – Higher precision collets ensure better machining results.
Use quality materials – Hardened steel collets last longer and resist wear.
Don’t overtighten – Excessive force can damage both the collet and the tool.
Maintenance and Care of Collets
To extend the life of your collets and tools:
Clean regularly – Remove chips, dust, and oil before use.
Check for wear – Replace collets with cracks or worn-out grips.
Store properly – Keep in a dry, organized case.
Use correct torque – Avoid overtightening to prevent distortion.
Rotate collets – Use different collets evenly to reduce wear on one piece.
Final Thoughts
A collet size chart is a must-have reference for machinists, CNC operators, and engineers. Choosing the right collet ensures precision, safety, and efficiency in your machining work.
Whether you’re using ER collets for CNC milling, R8 collets in a Bridgeport mill, or 5C collets for workholding, knowing the right size saves time and prevents costly mistakes.
So, before you start your next project, keep this guide handy. With the correct collet, your tools will last longer, your machine will run smoother, and your results will always be more accurate.
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