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ITEM OVERVIEW & IDENTIFICATION

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ITEM NAME:

Precision Gage Block Set (commonly known as "Jo Blocks" or Johansson Blocks)

ORIGINAL MANUFACTURER:

C.E. Johansson (CEJ) – Eskilstuna, Sweden

CALIBRATION / SERVICE ENTITY:

Webber Gage Division, The L.S. Starrett Company (Cleveland, Ohio, USA)

SET / MODEL NUMBER:

Set No. E 1 (Standard Imperial 81/85-Piece Master Reference Set with fractional & protector accessories)

ORIGINAL ACCURACY GRADE / QUALITY:

Grade A+ / Grade 2 (Calibrated under Webber / Starrett as Grade 2 / Working/Inspection Standard)

SERIAL NUMBER:

- Case Serial / CEJ Serial Number: 850675

- Owner Serial Number (Starrett Label): 51618

NATIONAL STOCK NUMBER (NSN):

- FSC 5210 (Measuring Tools, Craftsmen's)

- Applicable Military / Federal Spec NSN for standard 81-85 piece rectangular inch gage block sets:

* 5210-00-244-6101 (GAGE BLOCK SET, RECTANGULAR, INCH, 81/85-PC)

* Related Class NSN: 5210-00-543-2630 (Grade 2 / Inspection Grade)

STARRETT RE-CALIBRATION RECORDS (AFFIXED TO TOP LID):

- Inspection 1: Date 3/4/91 | Cert. Insp. No. 61890-A | Grade 2

- Inspection 2: Date 10/8/93 | Cert. Insp. No. 93-01731-A | Grade 2

- Inspection 3: Date 11/3/95 | Cert. Insp. No. 95-25224-A | Grade 2

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TECHNICAL SPECIFICATIONS

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- Type: Rectangular Slip / Gage Blocks

- Measurement System: Imperial (Inches)

- Material: High-carbon, high-chromium hardened tool steel (stabilized against metallurgical creep)

- Surface Hardness: Typically 64–66 HRC

- Surface Finish: Mirror-lapped to within ~0.4 to 0.8 micro-inches (0.01 to 0.02 µm) arithmetic roughness (Ra)

- Flatness & Parallelism: Held to within millionths of an inch (micro-inches / µin)

- Nominal Reference Temperature: 68°F (20°C)

- Wringing Capability: Blocks demonstrate molecular adherence ("wringing") when paired cleanly, holding together via atmospheric pressure, surface tension of trace oil/film, and intermolecular attraction.

TYPICAL 85-PIECE SET STEP BREAKDOWN:

- 4 Fractional Blocks: 1/16", 5/64", 3/32", 7/64"

- 4 Fine Incremental Blocks (.000025" steps): .100025", .100050", .100075", .1001"

- 8 Sub-thou Blocks (.0001" steps): .1002" through .1009"

- 49 Thousandths Blocks (.001" steps): .101" through .149"

- 19 Major Steps (.050" increments): .050" through .950"

- 4 Long Master Blocks (1.000" increments): 1.000", 2.000", 3.000", 4.000"

- Protector Blocks: .050" and .100" (often carbide or sacrificial hardened steel to protect stack ends)

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PRACTICAL / WORKSHOP USES

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1. Calibration Master for Dimensional Metrology:

- Primary physical standard for zeroing, setting, and checking micrometers, vernier calipers, dial indicators, bore gages, and depth micrometers.

2. Machine Tool Setup:

- Setting precise heights, stops, and reference planes on CNC mills, surface grinders, jig borers, and EDM tooling.

3. Sine Bar and Sine Plate Trigonometric Angles:

- Creating precise angular setups by stacking specific gage block heights under the rolls of a sine bar ($H = L \cdot \sin \theta$).

4. Inspection & Quality Assurance:

- Setting go/no-go plug, snap, and ring gages in metrology inspection rooms and toolrooms.

5. Coordinate Measuring Machine (CMM) Verification:

- Periodic 1D axis linearity and volumetric scaling checks.

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THEORETICAL & UNCONVENTIONAL USES

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1. Optical Metrology & Flatness Interference Standards:

- Used under monochromatic light with optical flats to generate light-band interference patterns (fringes) to calibrate flatness and film thickness down to nanometer/wavelength scales.

2. Demonstration of Surface Science & Intermolecular Forces (Wringing Physics):

- Academic demonstrations studying Casimir forces, van der Waals adhesion, and boundary-layer fluid mechanics between ultra-flat mirror-polished surfaces.

3. Thermal Expansion Coefficient (CTE) Experiments:

- Because standard steel gage blocks have an exact known CTE (approximately 11.5 × 10^-6 / °C), stacks are used inside dilatometers and thermal chambers to quantify thermal drift and environmental measurement uncertainty.

4. Acoustic & Ultrasonic Resonance Calibrators:

- Due to precise geometric thickness and known acoustic velocity in hardened steel, blocks can serve as discrete acoustic delay lines or thickness benchmarks for high-frequency ultrasonic transducers.

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Brand	Starrett
Instrument Type	Gage Block

CE Johansson Sweden Gage Block Set E1 Starrett Calibrated Jo Blocks Wood Box

Specifications