OK, this is what I found...
basically it varies from airport to airport.

I found US airports a security nightmare, it didn't matter what I did, what I wore or what I removed...I got "selected" for wanding, not just once, but repeated times, (palms up, palms down right foot forward, left foot forward, even up the kilt).
After 24 hours without sleep this process is annoying, even humiliating.
It put a very sour taste in my mouth for America and I will NEVER fly into LA again, it is the worst airport in the world for delays and poor staff attitudes.

British and Danish airports were much better with security, yes, even London.
The buckles in most cases didn't make a lot of difference, a quick explanation and maybe a quick wanding was all that was necessary.

If you really don't want to be wanded, wear velcro, but it makes little difference in the US, they do what they heck they want.

Naturally, sporrans must be removed, sometimes belts, don't wear a kilt pin and NEVER wear a sgian dhu, not even a plastic one. (altho, I did go thru Copenhagen airport and forgot about my kilt pin and nothing was said)