I'm having a hard time looking for something like this. I don't really know what they are called - so it's hard to search for.
Basically, need to have some wires exit a standard Hammond type case. And want to add some "strain relief" - and not just a hole in the case with wires coming out.
I found something kinda close searching for "Sleeved Grommet" - blah - not it.

But it's not exactly what I was looking for.
I was looking for something a lot like this:

Anyone point me in the right direction? What term should I be searching for?
They should be super cheap - I would think. Something like 100 for $10-$15 USD?
(And be installed like a grommet where it get locked into a hole drilled into the case.)