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Generally speaking, a machinist’s measuring tools receive the same level of protection and reverence as the Holy Grail. Every reader’s probably had his ears filled with endless tales of how the mechanisms of calipers and micrometers must be regularly oiled, protected from dust, and kept away from moisture. Not this set.

Mitutoyo’s model 500-752 is marketed as coolant-resistant, which is really something, considering that automotive coolant is a powerful oxidizer that quickly rusts any iron it touches. Not exactly stuff you want around your $150 (from Production Tool Supply) measuring instruments. Other features include inch/millimeter reading with 0.0005in/0.01mm resolution, auto-shutdown, and shatter-resistant (IP67 compatible) display. The waterproofing also makes the calipers dust-proof, and with a claimed three-year battery life, they’re not likely to suddenly crap out due to wear, abuse, or battery death.

A retailer called Reliable Paper is selling the set for $12 less than PTS, but they’re unrated according to Google’s product search.

500-752 [Mitutoyo]
Mitutoyo 500-752 [Production Tool Supply]
Street Pricing [Google Products]

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5 Responses to Coolant-Resistant Calipers

  1. Shopmonger says:

    Although Auto coolant may be a great oxidizer. I think they are probably referring to coolant from a cutter, grinder, or EDM machine, which cna be not only oxidizing but acidic in nature.

    Great for the those harsh situations non the less.


  2. Toolaremia says:

    Err… What? Automotive coolant is a powerful ANTI-oxidizer. Uh, that’s why we use it, to prevent corrosion in the cooling system. That, and it does a fine job of changing the boiling and freezing points of the mixture.

    Shopmonger is right-on here, the ‘coolant’ referred to is machine tool coolant.

  3. Lex Dodson says:


    Bloody Hell, I think you’re right. That’s what I get for not double-checking every single statement… But if automotive coolant is a deoxidizing agent, why does an iron plate spattered with the stuff wind up with rust spots where the coolant was? My impression was that ethylene glycol (the green stuff) wasn’t an oxidizing agent, and that’s why it’s used in iron-block engines, but propylene glycol (the orange stuff) was an oxidizer, and safe only in aluminum engines.

  4. Mrten says:

    Propylene glycol is used instead of ethylene glycol because ethylene glycol is pretty toxic (and dangerous because it tastes sweet). They are pretty similar in structure so I’d doubt one would be an oxidizer and the other wouldn’t be.

    It seems that ethylene glycol decomposes into acids, and it is these acids that cause the rust spots.

  5. BAMF says:

    These, like other “Coolant-proof” machinist’s tools are resistant to metalworking coolant. Metalworking coolant is rust-inhibitive by definition, but turns to the gummiest crap imaginable when it dries, eventually hardening almost completely.

    Any machinist that works with coolant-intensive processes, and has reached into a machine to take a measurement with some coolant still dripping onto the workpiece can attest to how nasty the stuff is when it works into a measuring tool.

    Coolant-proof tools also are usually much more dust-resistant as well, for those that don’t work with coolant often enough to warrant the price.

    Most machinists buy the $15 Harbor Freight digital calipers for dirty/harsh work, rather than risk their $150-200 Mitutoyo/Starrett/B&S units.

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