Sylvia Else wrote:
The obvious answer is that you bend the metal of the connector so that
it holds the wire in place.

This doesn't seem very satisfactory. Metal always retains some
flexibility, even when bent beyond its yield point. No matter how hard
you squeeze, there'll be some rebound when you release the pressure,
which should result in a loose joint.

After having had a bad experience trying to crip a lug some years ago, I
recently faced the need to do this again. So I bought a moderately
expensive ratchet based crimping tool. And, rather to my surprise, it
actually works.

But that doesn't answer the question of how.

Sylvia.

BTW, I'm seeing huge variation between lug types (same colour -
different brand). I bought some fully insulated ones - and could pull
them all off with no difficulty. The ones I had in my stock from way
back either failed by tearing the conductor - or had a strength
exceeding mine, and didn't fail.

At least there was some consistency - lugs out of the same box performed
the same as each other.

The crimping tool has a 'pressure' setting, but comes with no guidance
on how to decide which pressure to use.

Sylvia.