Precision Three-Point Internal Micrometer 2-6mm – Two-Point Expanding Probe for Small Bores

Description

I. In-Depth Product Analysis

Measuring internal diameters in the 2mm to 6mm range presents a unique set of metrology challenges. Traditional three-point internal micrometers are often too bulky to fit into such miniature bores, while standard two-point Calipers lack the precision and self-centering alignment required for accurate dimensional verification. Our H-375 Series Precision Three-Point Internal Micrometer bridges this gap with a clever, dedicated design. While it utilizes the high-precision screw and ratchet mechanism of a classic three-point micrometer, it features a specialized two-point expanding probe tip . This compact probe configuration provides the necessary clearance to access ultra-small diameters while delivering the exceptional repeatability and stability expected from a professional micrometer system.

The instrument is meticulously engineered for micro-precision applications. The ratchet thimble mechanism ensures that a consistent, non-varying measuring force is applied to the workpiece every single time. This eliminates the variable of human hand pressure, which is critical in the 2-6mm range where even microscopic variations in force can compress the workpiece or distort the thin probe arm, leading to inaccurate readings. The measuring contacts are tipped with hardened carbide , ensuring excellent resistance to abrasive wear when measuring hardened steels or abrasive materials in miniature components. Each measuring range comes paired with a dedicated precision calibration ring , allowing operators to instantly establish a traceable absolute zero baseline before taking critical measurements.

II. Technical Specifications

The H-375 series offers five precise ranges within the 2-6mm spectrum, each featuring the two-point expanding probe design, 0.001mm resolution, and matched calibration rings.

Technical Specifications:

Model Number	Measuring Range	Accuracy	Setting Ring	L Dimension
H-375-01-110	2 - 2.5mm	0.004mm	Φ2.5mm	12.5mm
H-375-02-110	2.5 - 3mm	0.004mm	Φ2.5mm	12.5mm
H-375-03-110	3 - 4mm	0.004mm	Φ4mm	22.5mm
H-375-04-110	4 - 5mm	0.004mm	Φ5mm	22.5mm
H-375-05-110	5 - 6mm	0.004mm	Φ6mm	22.5mm

Core Specifications:

• Resolution: 0.001mm

• Accuracy: 0.004mm (across all ranges)

• Probe Type: Two-point expanding mandrel design.

• Measuring System: Precision three-point internal micrometer structure.

• Measuring Faces: Wear-resistant carbide-tipped contacts.

• Operation: Ratchet thimble ensures consistent measuring force.

• Application: Suitable for both blind and through holes.

III. FAQ (Frequently Asked Questions)

Q1: Why does this micrometer use a two-point expanding probe instead of a standard three-point design?
A: At extremely small diameters (2-6mm), it becomes physically impossible to fit a full three-point wedge mechanism while maintaining the necessary clearance to reach the bottom of a blind hole. The specialized two-point expanding probe offers a clever solution: it retains the precision screw drive and ratchet mechanism of a three-point micrometer to ensure accurate linear advancement, but uses a compact two-contact expanding mandrel that easily fits into ultra-small bores. This combination provides exceptional stability and measurement repeatability where traditional three-point heads cannot physically enter.

Q2: What is the function of the included calibration ring?
A: The calibration ring is a precision-ground master standard with a known, exact internal diameter (e.g., exactly 4.000mm). Before measuring your precision workpieces, you insert the two-point probe into its matching calibration ring and use the SET function on the gauge to match the known diameter. This instantly establishes an absolute zero baseline that is traceable to a certified physical standard, ensuring reliable, accurate readings for all subsequent measurements.

Q3: How does the ratchet thimble improve accuracy in small bore measurements?
A: In micro-measurement ranges, the material of the workpiece and the size of the probe make them highly sensitive to measuring force. If you tighten the thimble by hand, you might apply too much force and compress the part or slightly distort the delicate probe tips, resulting in false undersized readings. The ratchet thimble automatically slips and clicks once the exact, optimal measuring force is reached, guaranteeing perfect repeatability across every measurement.

Q4: Is this micrometer suitable for measuring blind holes?
A: Yes. The two-point expanding probe design is exceptionally well-suited for blind holes. The contacts are positioned close to the flat face of the probe tip, allowing you to accurately measure the internal diameter almost down to the very bottom of the blind hole where the flat floor begins, without mechanical interference.

Q5: How do I maintain the delicate two-point measuring contacts?
A: The carbide tips are durable, but the probe arms themselves are miniature and precise. Always clean the contacts with a soft, lint-free cloth after each use to remove oil, dust, or metal chips. Never use the instrument as a "snap gauge" by forcing it violently into a hole; this can permanently bend the delicate expanding arms. Store the instrument in its protective case to prevent damage.

IV. Applications & Industry Uses

• Precision Instrument Manufacturing: Measuring the internal diameters of small pneumatic valves, miniature hydraulic fittings, and precision mechanical assemblies.

• Medical Device Manufacturing: Critical dimensional inspection of surgical instrument components, small catheters, and implantable medical parts.

• Watchmaking & Micro-Engineering: Precision verification of tiny gear bores, pivot holes, and watch movement components.

• Micro-Machining Centers: In-process and final quality checks for micro-drilled and micro-bored holes in aerospace and defense components.

• Quality Control & Metrology Labs: Used as a reference standard for checking small master setting rings and precise micro-fixtures.

• Research & Development: Measuring internal dimensions of prototype micro-devices and advanced composite materials.

V. Accuracy & Working Principle (Accuracy & Mechanics)

The H-375 series achieves a highly reliable 0.001mm resolution and 0.004mm accuracy through a precision mechanical screw-and-wedge amplification system. As the operator turns the ergonomic ratchet thimble, a high-accuracy threaded spindle drives a precision internal wedge mechanism forward. This wedge translates rotational movement into precise linear displacement of the measuring contacts. The two-point expanding probe design ensures that the contacts open uniformly, maintaining perfect alignment. The mechanical displacement is read directly from the engraved graduated scale on the thimble and sleeve. The ratchet stop guarantees that the measuring force is always perfectly consistent, ensuring repeatable results even when measuring extremely small, delicate components.

VI. Calibration & Maintenance

1. Daily Zero Check with Calibration Ring: Before each measurement session, clean the two-point probe contacts. Insert the probe into its matching calibration ring , gently tighten the thimble using the ratchet, and verify the reading matches the ring's engraved diameter. If not, use the zero adjusting wrench to realign the sleeve.

2. Clean the Probe Contacts: The two-point probe tips are microscopic and highly sensitive to debris. Carefully wipe the contacts with a soft, lint-free cloth immediately after each use. Do not use compressed air to blow out the probe, as this can force dust into the internal wedge mechanism.

3. Handle the Tool with Extreme Care: Because the 2-6mm measuring range requires such compact hardware, the two-point expanding probe is delicate. Always insert the tool gently into the workpiece. Never force it or jam it into a hole. Dropping the micrometer from a height can permanently warp the expanding mandrel.

4. Annual Professional Calibration: For strict compliance with ISO 9001 or AS9100 quality systems, the instrument must undergo formal traceable calibration by an accredited metrology laboratory every 12 months .