What size is a U drill bit?

If you're working in CNC machining, tool selection is everything — and choosing the right U drill bit size can make or break your operation. In this article, we’ll explain the standard size range of U drill bits, how to choose the right size for your application, and how U drill sizing compares to other drill types.

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What Is a U Drill Bit?

A U drill, also known as an indexable insert drill, is a high-performance tool used primarily for high-speed drilling, boring, and hole-making in metalworking. Unlike traditional twist drills, U drills use indexable carbide inserts and allow for faster feed rates and longer tool life.

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What Sizes Are U Drill Bits Available In?

U drill bits come in a wide range of diameters, typically starting from:

• Φ14mm (14mm)

• Up to Φ60mm or larger depending on the manufacturer

• Standard lengths are available in:

• 2D (2x diameter depth)

• 3D

• 4D

• 5D

For example, a 2D U drill with a 20mm diameter can drill up to 40mm deep.

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How to Select the Right U Drill Bit Size

When choosing a U drill size, consider the following factors:

• Hole Diameter: Match the drill bit diameter with the final hole size required.

• Hole Depth: Choose the appropriate L/D ratio (2D, 3D, etc.).

• Machine Power: Larger diameters require more torque and power.

• Insert Compatibility: Ensure your drill body fits standard insert types like SPGT, SPMG, etc.

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Common U Drill Bit Sizes & Applications

Diameter Range	Common Applications	Insert Type
14–25mm	Precision holes in automotive parts	SPGT inserts
26–40mm	General machining, boring	SPMG inserts
41–60mm+	Heavy-duty applications	Special insert holders

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Direct From Manufacturer: Custom & Standard U Drill Sizes Available

At [Your Company Name], we manufacture and supply high-quality U drill bits directly to global customers. Whether you need standard sizes or custom diameters, we offer full support with insert selection, tool holder compatibility, and fast delivery.

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✅ Key Takeaways

• U drill bits typically range from 14mm to 60mm+.

• Length-to-diameter ratios (2D to 5D) define drilling depth.

• Choosing the correct size depends on hole specs, machine capabilities, and insert type.

• Manufacturer-direct sourcing offers better pricing and customization options.

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Need Help Choosing the Right U Drill Size?

Contact our engineering team for a free consultation on U drill selection and insert compatibility.