Mitutoyo 511-721-20 Standard Dial Bore Gauge, 18-35mm

Technical Overview

Mechanical standard bore gauge set for 18–35mm ID. Features ±2µm accuracy, 0.001mm graduation, 100mm depth, and 50% operator hand heat isolation.

Key Features

Self-centering bridge ensures quick, automatic centering inside the bore for reliable alignment
Hollow-structured, enlarged grip reduces the influence of thermal expansion from the operator's hand by 50%
Highly durable and abrasion-resistant carbide ball tips on both the contact point and anvil
Comes complete with 2109AB-10 dial indicator (0.001 mm resolution) and 21DZA000 protective cover
Supplied with 9 interchangeable anvils and 2 spacers (washers) to configure measurements in small steps
Ensures high accuracy (±2 µm) and exceptional repeatability (0.5 µm)
Enables measurements up to a probing depth of 100 mm

Technical Specification Matrix

Parameter	Value
Measuring Range	18 - 35 mm
Graduation	0.001 mm
Accuracy	±2 µm
Repeatability	0.5 µm
Indication Stability	1 µm
Probing Depth	100 mm
Measuring Force	4 N or less
Guide Force	6 N or less
Stroke of Contact Point	1.2 mm
Number of Anvils	9
Number of Spacers	2
Dial Indicator Model	2109AB-10
Dial Protection Cover	21DZA000
Stem Diameter	8 mm
Contact Point Material	Carbide
Physical Weight (kg)	0.33
Dimensions L x W x H (cm)	28.2 x 5.7 x 3.5

Industrial Applications

1. Automotive Engine Valve Guide and Cylinder Inspection

Rebuilding high-performance combustion engines requires verifying the inner diameter of valve guides and small cylinder bores (typically within the 18–35 mm range). This tool's 100 mm probing depth allows full axial travel through the cylinder, and the 0.001 mm resolution ensures that minute taper or out-of-roundness anomalies are detected, preventing engine failure or oil leaks.

Problem Solved

Solves the issue of detecting micro-level taper (bell-mouthing) and ovality in engine valve guides and small cylinders, which cannot be measured with standard calipers.

Valve Guide OvalityCylinder Taper MeasurementOut-of-RoundnessID Metrology

2. Precision Hydraulic Actuator Bore Quality Control

Hydraulic valve bodies and cylinders operate under extremely high pressures, requiring tight clearance fitment of the pistons/spools to prevent hydraulic fluid bypass. Using the Mitutoyo 511-721-20, operators can check the bore diameters (18–35 mm) of the actuator housings to an accuracy of ±2 µm, ensuring consistent tight-tolerance machining.

Problem Solved

Prevents internal hydraulic fluid leakage by ensuring the machined housings meet exact concentricity and diameter tolerance requirements before final assembly.

Hydraulic Actuator BoresClearance Fit VerificationTight Tolerance Quality ControlBore Concentricity

3. High-Speed Spindle Shaft Bearing Seat Verification

Bearings in high-speed CNC machine spindles require precise interference fits to prevent rotation of the outer bearing race in the housing. This gauge is used to measure the ID of the bearing journal housings (within 18–35 mm) prior to press-fitting the bearings. The 50% thermal heat isolation of the grip ensures that thermal expansion from the operator's hands does not distort the delicate micro-level measurements during batch checks.

Problem Solved

Eliminates bearing seat dimension distortion caused by operator hand heat transfer during high-volume QA/QC measuring processes.

Bearing Journal HousingInterference Fit MeasurementThermal Isolation MetrologySpindle Assembly QA