MAG-ic Probe Electronic Thickness Gauge

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MAG-ic Probe Electronic Thickness Gauge

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MAG-ic Probe Electronic Thickness Gauge

About This Item

Works where a traditional caliper can't! Advanced, convenient way to measure the thickness of instrument tops and backs for graduating.

Unlike a traditional mechanical caliper, MAG-ic Probe's electronically calibrated magnet-based design works for assembled instruments, too—it's easy to measure prized instruments and replicate their specs in your own builds.

Downloadable software lets you record your measurements directly to your computer on a photo or drawing of your instrument—very handy!

Each MAG-ic Probe utilizes a wired sensing wand (the probe) that electronically measures the distance to the magnet. As the probe samples the upper surface of an instrument top or back, the magnet follows the sensor on the inside surface, jumping over braces and tone bars. This provides a continuous readout of the wood thickness in thousandths of an inch (mils) or millimeters, accurate to 0.1mm. The effective range of measurement is 0.0" to 0.6" ( 0-15mm). Two magnets are included, a larger one for guitars and large instruments, and smaller one for mandolins, ukuleles and small instruments.

Bonus: Downloadable MAG-ic Probe software lets the probe work with your Windows or Mac computer via a USB connection. You can upload a JPEG photo or drawing of your instrument, and record your measurements directly on it, to save or print. See System Requirements below.

#4101 MAG-ic Probe is a portable outfit. It includes a 9-volt battery-operated handheld unit with LCD readout, plus a plug-in probe with magnets. A USB cable is supplied for attachment to your computer, to use with downloadable MAG-ic Probe software if desired. Battery included.

System Requirements
Works on Windows and Mac computers, learn more and download the software at

Warning! MAG-ic Probe uses seriously strong rare earth Neodymium spherical magnets. Keep them away from other electronic equipment, guitar pickups, pacemakers and children.


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  • 4.67 average rating from 3 reviews
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(Customer's Reviews)

It can guide me to taper the edge of the top. At the same time, measuring the other tops for reference. As a fact, the bass part improves a lot after tapering.



(Customer's Reviews)

I tested the MAG-ic Probe against a digital caliper that is accurate to the nearest .001 inch, and found they both agreed in the range that applies to guitar plate thickness. I don't have a Hacklinger gauge, but this tool is clearly less expensive and does not involve estimating. The only drawback is that typical steel stringed braces (.5 inch tall) are too high for it to "jump". Instead, I must place the ball with one hand inside the instrument and locate the probe above it on the outside with the other. Still, it is the best system available for taking measurements on a box that has been closed, and it has the advantage of coming with software that lets you record the data for each instrument you wish to archive. It appears that the physics of magnets, their weights and strengths, and the law of gravity do not permit creating a device that will easily jump tall braces, but it handles up to 3/8 inch tall braces well. Like Stew-Mac, the MAG-ic company stands behind its product, and is very helpful if you have questions or concerns. If you like to make adjustments to the thickness of your soundboards after the box has been closed, this tool will remove a lot of the anxiety associated with that process, and likely lead to a better outcome. Likewise, if you are interested in the study of existing instruments, it is an invaluable aid.



(Customer's Reviews)

Easy to use with the bottom open and off the guitar. Accurate measurements, but beware of steel wool dust. If you get iron dust on the ball the measurements will be off, I use adhesive tape to clean the ball and do the measurement's before I use steel wool now. I can imagine that the will be problems using the magnetic ball on a guitar with a metal pickup. Hard to get the ball loose! My biggest problem was to get the lid off the battery compartment... Instructions how to calibrate and use the instrument is written on the battery unit, so that was not hard to learn. This instrument solved my problem to get accurate thickness on the guitar top when doing a renovation.

StewMac PDF Catalog, page 25 See MAG-ic Probe Electronic Thickness Gauge
on page 25 of our StewMac Catalog PDF

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