I'll start off with my question:
-- Is my understanding of inductors wrong, or
-- Is my $20 eBay component identifier failing me as an L meter?
Here's what I did: I wrapped a (presumably steel) nail with Kapton tape, and then wrapped a whole bunch (est. 250) of windings of enamelled copper wire around it. De-enammeled the ends with a flame, plugged it into my cheap meter, and it reads 0.7 ohms + 0.09mH. So, then I add a steel screwdriver touching both ends of the nail (yes, the nail was bent to enable this). I was expecting the screwdriver to "complete the magnetic circuit", increasing the permeance* and thus increasing the inductance. Yet, I take another reading with the meter, and it reads 0.7 ohms + 0.09mH... exactly the same as before. Am I down in the noise floor of the component identifier, or am I wrong to expect a change in inductance? I feel like gapped transformers have a lower mutual inductance because the gap sorta ""breaks"" the magnetic circuit, and was expecting a similar effect here.
* (I am in no way qualified to use this term with such confidence)