In uk.d-i-y, D.M. Procida wrote:
I want to make an unopenable jam jar - one that will resist the
strongest grips.

What's the best way to achieve this?

I imagine that filling it up with boiling water, running a seam of
superglue along the rim and thread then screwing the lid on tightly
would get the best results.

I'd remove the soft sealing ring from inside the lid, the use a good
quantity of Araldite and cure it in the oven.

--
Mike Barnes