Very nice.
In my opinion, washers are more ubiquitous than metal plates and may have a final form factor that is easier to conceal.
Yet, your solution is perfect, as it uses commonly available materials and preserves the holder's privacy.
Of course, the weakest link in my guide is the jig, which is necessary for my method, while you found an excellent alternative for those who haven't been able to find one.

Security models are very different as different attack vectors are possible: there isn't a "better solution" for everyone as scenarios are different for everybody. This guide is excellent for those who want to rely on pieces you can find in any hardware store.

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