Three-Point Internal Micrometer 50-300mm – Self-Centering Bore Gauge with Carbide Tips & Aluminum Body

Description

I. In-Depth Product Analysis

Measuring internal diameters on large-scale components—such as heavy engine cylinders, large hydraulic actuators, and industrial pipes—requires a tool that not only delivers exceptional accuracy but is also practical for an operator to handle over long inspection sessions. Our H-315 Series Three-Point Internal Micrometer is specifically engineered for these demanding tasks.

Unlike solid steel frames which can become prohibitively heavy at this scale, this series features a precision-machined aluminum body . The aluminum construction significantly reduces overall weight, minimizing operator fatigue and making it far easier to maneuver the instrument around large workpieces. Additionally, aluminum's excellent thermal conductivity helps the tool reach ambient temperature faster than steel, reducing the risk of thermal expansion affecting the 0.005mm to 0.007mm accuracy during prolonged handling.

At the core of the instrument is the self-centering three-point contact system . As the thimble is rotated, three precision-ground wedges expand outward at identical rates, automatically locking the gauge into perfect alignment with the absolute centerline of the bore. This completely eliminates off-angle errors commonly associated with two-point Calipers , ensuring accurate measurement of ovality and taper. The measuring contacts are tipped with hardened carbide , providing exceptional wear resistance against the abrasive surfaces of cast iron, steel pipes, and rough-machined parts. For measurements up to 100mm, dedicated precision calibration rings are included to establish a traceable zero baseline. For ranges exceeding 100mm, setting rings are available as optional accessories.

II. Technical Specifications

The H-315 series for the 50-300mm range is available in multiple configurations, all featuring the lightweight aluminum body, carbide tips, and a standard 150mm extension rod.

Technical Specifications:

Order Number	Measuring Range	Accuracy	Setting Ring	L1 Dimension	Extension Rod
H-315-10-270	50 - 63mm	0.005mm	Φ62mm	114mm	150mm
H-315-11-270	62 - 75mm	0.005mm	Φ62mm	114mm	150mm
H-315-12-270	75 - 88mm	0.005mm	Φ87mm	114mm	150mm
H-315-13-270	87 - 100mm	0.005mm	Φ87mm	114mm	150mm
H-315-61-070	100 - 125mm	0.005mm	Φ100mm	145mm	150mm
H-315-62-070	125 - 150mm	0.005mm	Φ150mm	145mm	150mm
H-315-63-070	150 - 175mm	0.005mm	Φ150mm	145mm	150mm
H-315-64-070	175 - 200mm	0.005mm	Φ200mm	145mm	150mm
H-315-65-070	200 - 225mm	0.007mm	Φ200mm	145mm	150mm
H-315-66-070	225 - 250mm	0.007mm	Φ250mm	145mm	150mm
H-315-67-070	250 - 275mm	0.007mm	Φ250mm	145mm	150mm
H-315-68-070	275 - 300mm	0.007mm	Φ275mm	145mm	150mm

Core Specifications:

• Measuring Faces: Hardened carbide tips.

• Body Material: Lightweight aluminum construction.

• Operation: Ratchet thimble mechanism for consistent measuring force.

• Design: Self-centering three-point contact for automatic alignment.

• Calibration Rings: Included for models up to 100mm (optional for models above 100mm).

• Included: 150mm extension rod for deep hole measurements.

III. FAQ (Frequently Asked Questions)

Q1: What is the advantage of the aluminum body in a large-bore micrometer?
A: When measuring diameters over 100mm, the physical size and weight of the instrument can become a major factor in operator fatigue. The precision-machined aluminum body significantly reduces the overall weight compared to traditional steel frames, making the micrometer much easier to handle, position, and maneuver around heavy, oversized workpieces. Additionally, aluminum's thermal expansion properties allow the tool to stabilize quickly to ambient workshop temperatures, reducing thermal drift.

Q2: How are calibration rings handled for ranges over 100mm?
A: Calibration rings are included as standard equipment for all H-315 series models up to 100mm to ensure you have a traceable zero baseline right out of the case. For the larger ranges measuring 100mm to 300mm, setting rings are available as optional accessories . This ensures cost-effectiveness for labs that may not require daily validation at these extreme dimensions, while still offering full traceability when needed.

Q3: Why are carbide measuring faces used on these large heads?
A: At this industrial scale, you are frequently measuring rough castings, uncoated steel pipes, and heavy machined surfaces. These abrasive materials will rapidly wear down standard steel measuring faces, causing them to lose their perfect spherical geometry and leading to measurement drift. The hardened carbide tips provide exceptional wear resistance, ensuring that the 0.005mm to 0.007mm accuracy is maintained over years of heavy-duty service.

Q4: Can this micrometer measure deep holes?
A: Yes. Every model in this series comes with a standard 150mm extension rod. This allows you to securely extend the measuring head deep into large hydraulic cylinders, engine block water jackets, or long industrial piping while keeping the micrometer head and thimble easily accessible and readable outside the bore.

Q5: Is the ratchet thimble necessary on such a large tool?
A: Absolutely. At these larger diameters, the force you apply can vary significantly if done by hand. Excessive pressure can slightly compress the measuring contacts or distort the workpiece. The ratchet thimble ensures that the exact same, optimal measuring force is applied every single time, guaranteeing flawless repeatability and eliminating the variable of operator hand pressure.

IV. Applications & Industry Uses

• Large Bore Machining & Inspection: Precise verification of bored and honed holes in large CNC-machined components.

• Automotive Engine Manufacturing: Measuring deep cylinder bores in heavy-duty diesel and marine engines.

• Hydraulic Cylinder Manufacturing: Inspecting the internal diameters of large hydraulic actuators, pneumatic cylinders, and industrial pressure vessels.

• Aerospace Component Measurement: Verifying internal dimensions of large structural tubing and precision-machined cast alloy parts.

• Heavy Equipment Manufacturing: Critical dimensional checks on industrial gear housings, large bearing seats, and machinery frames.

• Quality Control & Precision Metrology : A professional reference standard for verifying large master setting rings and custom production fixtures.

V. Accuracy & Working Principle (Accuracy & Mechanics)

The H-315 series achieves its precise 0.005mm to 0.007mm accuracy through a robust mechanical wedge amplification system. Inside the lightweight aluminum measuring head, a high-accuracy threaded spindle drives three precision-ground wedges forward as the operator rotates the thimble. Because these wedges are machined to exact equal angular tolerances, they force the three carbide measuring contacts to expand outward radially at identical rates. This synchronized expansion guarantees flawless self-centering alignment with the true centerline of the bore. The ratchet thimble ensures that the measuring force applied is perfectly consistent and repeatable. The final reading is derived from the precision engraved graduations on the thimble and sleeve, translating the spindle's precise linear displacement into a clear, easy-to-read internal diameter.

VI. Calibration & Maintenance

1. Daily Zero Check: For models up to 100mm, clean the measuring contacts and insert the head into the included calibration ring . Gently tighten using the ratchet thimble, and use the zero adjusting wrench to align the zero line. For models over 100mm, use an optional setting ring or a calibrated master gauge fixture to verify the zero point.

2. Clean the Contacts: After each use, carefully wipe the three carbide measuring contacts with a soft, lint-free cloth. Any metal chips, oil, or abrasive dust left on these precision surfaces will directly affect the accuracy and scratch the workpiece.

3. Protect the Aluminum Body: Although lightweight, the aluminum body should be handled with care to avoid dents. Always store the tool securely in its protective case when not in use. Avoid exposing it to extreme temperatures.

4. Annual Professional Calibration: For strict compliance with ISO 9001 or AS9100 quality standards, the entire instrument should undergo a full, traceable calibration by an accredited metrology laboratory every 12 months .