Can’t answer for aviation but I worked in the general testing and certification industry (Underwriters Laboratories) with tons of rules and externally audited standards about calibration of measurement and test equipment.

Yes, things like rulers and gauges are tested. The schedule depends on the use case and frequency of use. For relatively light lab duty stuff, rulers and gauges were checked 1-2 times a year. Things that are used more frequency or more aggressively are checked more often.

In theory, yes. In practice, they get dirty and bent faster than they wear out.

They're cheap. Shops that care have them on a replacement schedule.

In aerospace everything like that is traceable and calibrated on a schedule. Traceable means that there is paper work that shows what it was calibrated against. Which itself is traceable to a NIST standard. The difference between traceable and ordinary measurement equipment is a couple of extra $.

Put is this way one time I found a set of hex torque drivers with cal stickers on them at a surplus place. So when I say everything I do mean everything. So yeah a feeler gauge should be traceable.

Yup. Traceable all the way back to the batch of material the part is made of. For every part in the plane. One of my customers makes parts for Rolls-Royce engines for the aviation industry and have to store certs and manufacturing records for even the smallest part. That includes certs on each step of manufacturing and material. Its pretty intense! During crash investigations they can be called upon to provide the full audit trail. Now imagine the amount of paperwork that is produced during an investigation when every nut and spring in a plane has the same amount of associated paperwork produced.

>The difference between traceable and ordinary measurement equipment is a couple of extra $.

This idea again. I don't know why people are saying this. It's not true. Aviation you're allowed to use any tool you want unless the workshop manual says to use a specific tool.

OEM calibration certs are useless to an aviation company because it's someone else promising accuracy that could see you thrown in jail if it's wrong. Before tooling is used the first time it will be calibrated. Then calibrated again at set intervals.

>hex torque drivers with cal stickers

It's most likely the part had stickers so it was in their system for visual inspection for good condition. I have a pair of lockwire pliers that were pulled from the shop floor due to them being indicated worn during a visual inspection. I still have them 7 years later and they're still the sharpest pliers I own.

As for the traceability from birth, this applies to parts that go on the aircraft not tooling. Tooling traceability you need to know what tool was used if it's required to be calibrated. ie torque wrenches.

They are typically harden steel, so wear minimally and when you test a gap, you’re not really applying much force.

If the feeler gauge doesn’t slip in with minimal force, then that tells you the gaps is smaller than the gauge.

> If the feeler gauge doesn’t slip in with minimal force, then that tells you the gaps is smaller than the gauge.

The numbers of sets of comically bent out of shape feeler gauges I've encountered in my life demonstrates that there's a bunch of folks out there who don't understand how they're supposed to be used. As in "maybe if I just push harder this'll fit" :)

It’s a combination feeler gauge/pry bar!

Yes. And places that deal with these types of tolerances will typically have a person who's job is to simply verify and replace gauging. If a gauge doesn't have a documented test verifying its accuracy, then it has to be assumed to be inaccurate and any parts or tests based on results provided by the instrument need to be redone or the part scrapped.

For things to measure, where a person finally have to sign for an OK, tools allways have to be calibrated and tested (not just in aerospace industrie). Thats also the reason, why there is not just the persons name but also the toolnumber on the test protocol.