Digital Micrometer for Scratch Depth, 8400K, by J Chadwick Co.

A time-saving maintenance tool to measure width and depth of scratches. Repeatable Results ● Save Time ● Save Parts ● Eliminate Guess
8400K Digital Micrometer for Scratch Depth
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The 8400K Digital Optical Micrometer is a unique coating and surface inspection tool that offers speed, precision, and repeatability. Scratch depth measurement used to be an art. With the 8400K, you can now do it in less than 20 seconds. This time-saving tool was designed specifically for measuring the width of scratches and vertical depth of surface features. "Visual inspection" is standard for any component with scratch or corrosion pit damage, and maximum allowances are often specified. Other methods of visual inspection are time consuming and inconclusive.

The 8400K lets you measure the width of scratches using the reticle eyepiece and vertical depth of surface features, usually to evaluate the severity of mechanical damage such as scratches, corrosion, pits or blemishes difficult to observe by other methods. Accurate measurement is essential to determine whether a part should be kept in service, and the 8400K brings remarkable precision and integrity to this judgment process.

The 8400K is designed for use in the field. The sealed, non-magnetic case is dustproof and shock-resistant to withstand everyday shop use.


  • Exact and repeatable. Very specific tolerances often apply to surface damage and exact measurements are essential todetermine if a part should remain in service. The 8400K allows “repair or replace” maintenance decisions to be made with absolute certainty, and backed up with precise measurement data.
  • Eliminate Guesswork. Quickly and confidently perform visual inspections and make real assessments of damage severity.Avoid using substandard parts or scrapping parts that are still within safety and tolerance limits.
  • Portable and Versatile. The kit has interchangeable bases and lenses for use on almost any surface, including transparencies and composites. Use one tool to inspect many types of damage; corrosion pitting, scribe lines, bubbles, crazing, and scratches on parts.
  • Simple Operation. Unlike analog models, the 8400K is repeatable and requires no manual calculations. The digital LCD display is easy to read and toggles between inches and millimeters. Optional accessories allow data to be exported to a PC or handheld device.

Inspection for Scratches, Corrosion & Wear

  • Measure scratches with accuracy and repeatability. Depth allowances are often specified, but proper measurement is needed to determine if a part should be kept in service. The 8400K performs this task quickly and easily, where other methods are time consuming and inconclusive.


  • Measurement Technique: First, focus on a smooth surface next to a scratch. Then, zero out the digital display (you can choose a readout in either inches or millimeters). Next, focus on the bottom of the scratch. The digital display shows depth relative to the surface. "Floating Zero" means that no arithmetic is necessary to arrive at the result. If you can focus, you can perform cost-saving, accurate measurements of surface damage to mechanical parts.
  • Applications:  Coated surfaces, windshields and other transparent materials may be measured for overall thickness, depth of crazing, and depth and width of imbedded bubbles or seeds as well as scratches. Shafts, couplings, airframes, masts, castings, windshields, fuselage skin (pitot tube area), leading edges, paint, turbine blades, fuel pump gears, props, rotor blades, sealing surfaces and much more.
  • Options: The 8400K can output to a printer with Statistical Process Control (SPC), or be linked to a PC. These options provide hard copy for documentation, traceability, and trend monitoring.
Principle of Operation

The 8400K measures the distance between two points, or regions of interest (ROI). Clear, accurate results are produced in three easy steps:

  • Step 1 is to focus on the first ROI, generally the good surface next to a scratch or pit.
  • Step 2 is to set the display to zero with the touch of a button when the first ROI is in sharp focus.
  • Step 3 is to focus on the second ROI, the bottom of the scratch or pit. When the second ROI is in sharp focus, the depth of the scratch (distance between the two points) is shown on the digital LCD display.

    Read and record the results - or export directly to a PC spreadsheet or hand held processor  (requires optional accessories). It’s that easy and takes less than a minute!

Accuracy &

In inches:
The digital readout shows four places right of the decimal: "0.0000"
The far right (ten-thousandths) reads "0" or "5" (0.0000 or 0.0005)
Accuracy: 0.001"
Resolution: 0.0005"

In millimeters:
The readout shows "0.00". The far right (hundredth of mm) place reads in 0.01 mm increments.
Accuracy: 0.01 mm
Resolution: 0.01 mm

Depth & Width
of View

With 10X eyepiece:
Vertical range (or depth): 0.250" (6.4 mm) from surface to bottom of scratch.
A width of 0.040" (1.0 mm) can be measured with reticle eyepiece.

With 4X eyepiece:
Vertical range (or depth): 1.250" (32 mm)
A width of approximately 0.150" can be viewed (but not measured).


Hardwood case: 16" x 7" x 5"
Micrometer only: 2" dia. x 9" height (3" dia. at base)


Accuracy: ±0.001" (±0.02 mm)
±0.001" (±0.02 mm)
Width: 0.040" (1.0 mm)
Measured surface must be perpendicular to micrometer.
Use only 10X objective lens with reticle eyepiece.

& Weight

Micrometer with base: 3" dia x 9" height, 1.5 lbs
Kit in case: 13" x 11" x 6" (L x W x H), 7 lbs

Included in 8400K Micrometer Kit


Part No.



Digital Optical Micrometer with LCD display
3-Leg Base with plastic tipped feet to protect surface finish
4-Leg Base
V-Block Base
20X Eyepiece
10X Eyepiece with reticle scale for visual width measurements
10X Objective Lens
4X Objective Lens
23 LED Flashlight
Foam-lined ABS plastic case
Scratch Sample Plate for training and demonstration
Allen Wrench, Spare Batteries Manual, Calibration Certificate


The 8400K Micrometer can download data to a small printer or to your PC. These capabilities are important for keeping documentation and traceability procedures, and for monitoring trends.

DP-1HS Digimatic Mini-Processor & Printer

This is the most popular 8400K option. A one-meter cable connects the 8400K to this instrument, which is capable of printing, storing and processing measurement data. Tolerance judgments, statistical results and histograms may be printed. When limits are set, up/down arrows appear for exceeded limits. There are several types of printouts to choose from. Readings can either be printed in the order they are taken, or plotted according to their magnitude in a number of statistical chart formats.
  • Weight: 1.1 lbs.
  • Dimensions: 7.1" X 6.3" X 3.2"


Input Tool for Personal Computers

Two cables allow data to be sent to a spreadsheet program such as Excel. Measurements are entered with just one touch of a data button. No battery or AC power is needed, and laptops can be used. The cables have small interface boxes in the middle. One cable connects via the keyboard input port (keyboard is disabled), the other through the RS-232 port.

  • Dimensions (both styles):
  • Cable Length: 40"
  • Total Weight: 87g
  • Center Box: 2.4" X 1.5" X .9"
  • RS-232 Cable : P/N 264-005
  • Keyboard Cable: P/N 264-007