Professional Large Range Inside Micrometer Set 100-2100mm – 0.01mm Resolution with Calibration Ring & Optional Carbide Tips

Description

I. In-Depth Product Analysis

When measuring internal diameters in large-scale manufacturing—such as heavy machinery cylinders, pressure vessels, and large engine bores—standard internal micrometers often lack the reach and stability required for precise readings. The H-302 Series Inside Micrometer Set is engineered to solve this challenge with a versatile, highly stable modular system.

At the core of this instrument is the precision-machined micrometer head , featuring a 25mm (1″) measuring travel and a clear 0.01mm (0.001″) resolution. The kit includes multiple Φ22mm solid steel extension rods of different lengths (25mm, 50mm, 100mm, 200mm, and 400mm). By combining these rods, you can achieve precise measurements across the entire 100-2100mm range. The Φ22mm rod diameter is a critical feature; this thick, heavy-gauge steel construction significantly reduces the bowing and deflection that plague thinner rods at extended lengths, ensuring the measurement reading reflects the true internal diameter rather than rod flex.

Each set includes a precision calibration ring . This certified ring allows operators to instantly set the zero point of the micrometer head before measuring, ensuring absolute traceability to a known physical standard. For demanding applications requiring continuous measurement of abrasive materials like cast iron or uncoated steels, users can upgrade to optional carbide-tipped measuring faces (Model 302-XX-070), which drastically extend the lifespan of the contact points and maintain pin-point accuracy over years of industrial service.

II. Technical Specifications

The H-302 series offers six standard set configurations, allowing you to choose the precise length coverage your facility requires.

Core Specifications:

• Travel of Micrometer Head: 25mm / 1″

• Resolution: 0.01mm / 0.001″

• Accuracy Formula: (3 + n + L/50) μm (Where * n * = number of extension rods used, L = maximum measurement length in mm).

• Extension Rod Diameter: Φ22mm (Solid Steel Construction)

• Optional Upgrade: Carbide measuring faces (Order Model: 302-XX-070)

III. FAQ (Frequently Asked Questions)

Q1: What is the advantage of the Φ22mm steel extension rods?
A: When measuring large internal diameters over 500mm, the length of the extension rods makes them susceptible to bending or deflection under their own weight. The Φ22mm diameter ensures exceptional rigidity and structural stability. This thicker steel shaft dramatically reduces flex errors, guaranteeing that your final measurement accurately represents the true internal diameter instead of a distorted reading caused by a sagging rod.

Q2: Why is a calibration ring included in this set?
A: The calibration ring is an exact, precision-ground master standard with a known internal diameter (for example, exactly 100.000mm). Instead of relying on a separate gauge block setup, you simply assemble the micrometer head, insert it into the calibration ring, and lock the "zero" position on the thimble. This guarantees a perfectly traceable zero point for all subsequent production measurements.

Q3: What does the accuracy formula "(3 + n + L/50) μm" mean?
A: This formula outlines the maximum permissible error based on your setup. "n" is the total number of extension rods you are using to reach the target diameter, and "L" is the total measuring length in millimeters. For example, if you use 4 extension rods to measure a 1000mm bore, the maximum error would be (3 + 4 + 1000/50) μm = 27 μm (0.027mm). This mathematically guaranteed accuracy ensures reliable data for structural engineering and quality control.

Q4: When should I choose the optional carbide measuring faces (Model 302-XX-070)?
A: Standard steel measuring faces can become worn and flattened over time when repeatedly measuring hard, abrasive materials like cast iron components, rough steel pipes, or sand-cast housings. Upgrading to the optional carbide-tipped faces significantly improves wear resistance and maintains the precise spherical geometry of the contacts, ensuring lasting accuracy in high-volume, heavy-duty measurement environments.

Q5: How are the extension rods assembled and disassembled?
A: Each extension rod features precision-threaded ends that screw securely into the micrometer head or into each other. The threading ensures perfect coaxial alignment, so the rod remains perfectly straight with the micrometer axis. When disassembling, always use the flat spanner wrench included in the set to tighten or loosen the rods to avoid damaging the fine threads with pliers.

IV. Applications & Industry Uses

• Heavy Industrial Machinery: Measuring large bored holes inside manufacturing machines, press frames, and industrial gear housings.

• Pipe & Pressure Vessel Inspection: Verifying the internal diameters of oil and gas pipelines, large-diameter flanges, and industrial pressure tanks.

• Energy Industry: Internal measurement of turbine casings, hydraulic actuator cylinders, and large electric motor housings.

• Aerospace & Heavy Equipment: Inspecting internal dimensions of landing gear components, large structural tubing, and heavy casting housings.

• Automotive & Marine Engine Rebuilding: Checking the internal diameters of oversized marine engine cylinders and large diesel engine blocks.

• Quality Control (QC) Laboratories: A standard set for verifying the internal sizes of master gauges, setting rings, and large precision fixtures.

V. Accuracy & Working Principle (Accuracy & Mechanics)

The H-302 series achieves its precise readings through a classic micrometer screw and interchangeable rod system. The measuring head features a highly accurate threaded spindle with a pitch of 0.5mm. As the operator rotates the thimble one full turn, the spindle advances exactly 0.5mm. With 50 divisions on the thimble, the resolution is 0.01mm . To measure large bores, the operator combines multiple Φ22mm steel extension rods with the micrometer head until reaching near the target bore diameter. The fine adjustment is then completed using the micrometer head's spindle. The system relies on precise mechanical alignment; because all extension rods are machined to exact lengths and screwed together securely, the measurement is simply the sum of the rods used plus the reading on the micrometer head.

VI. Calibration & Maintenance

1. Zero Check Using Calibration Ring: Upon receiving the set and before every major measurement task, assemble the micrometer head (and any required base rods). Insert it into the included calibration ring , and gently adjust the thimble until the contacts touch the inner wall. Use the locking screw to fix the reading and verify the zero point.

2. Rod Maintenance & Storage: The Φ22mm steel extension rods must be kept clean and lightly oiled to prevent rust on the precise threads. Always store the rods properly in the designated slots in the wooden case to prevent bending or scratching. Never force a rod into the case; ensure the foam insert is properly aligned.

3. Clean the Threads: Before assembling rods, wipe the male and female threads with a soft cloth to remove dust or grit. Cross-threading these precision parts can permanently damage the thread quality and ruin the coaxial alignment.

4. Professional Calibration: For ISO 9001 or AS9100 compliance, we strongly recommend sending the complete set to a certified metrology laboratory for full traceable calibration every 12 months to ensure the (3+n+L/50)μm accuracy specification is fully maintained.