Hello
AC electrical wire protection ITEM to join at the box. I know this is a noob question. What do you call the small rubber or plastic unit that protect the AC wire where it meet the project box? I kinds of hold and protect the AC wiring going into the wood/plastic box. This is for a 2 wire non ground flexible ac wire.
The general term I would use is strain relief. Something that is only intended to protect the wire from abrasion and not keep it from being yanked out of its connections would be more of a grommet.
The specific type of strain relief component I really like are called "cable glands".
Great! Thanks 
Also search for "cordgrip".
A cable gland is unsuitable, they are huge and designed to seal hermetically. Use a strain-relief grommet. Sometime like this: https://www.rapidonline.com/Anixter-3001150-Strain-Relief-Bush-6-4-7-4mm-Cable-04-0262?IncVat=1&pdg=pla-339154412538:kwd-339154412538:cmp-757438067:adg-44804851896:crv-207912323492:pid-04-0262:dev-c&gclid=CjwKCAjww6XXBRByEiwAM-ZUIMoUfMQxzKTi0ZLKIAyHH6oE3CJVSPf3dutB8xNcmfMDo7Y8z_atNhoCtN0QAvD_BwE
MarkT:
A cable gland is unsuitable
How can you judge suitability without knowing the application?
MarkT:
Sometime like this:
I despise those things.
pert:
I despise those things.
Yes, they need a non-round hole, which is difficult to achieve without the proper tools. Also they are unsuitable for a wooden box or many other hobby materials.