No - most office chairs are stem mount. this caster is plate mount.
I used #6 self drilling 1 1/4"
not square, 1' in one direction, don't remember other (1&1/2"?).
The description does nor indicate they can be used out doors. The finish on the metal part does not look like it has any rust proofing on it.
Mine are outdoors and have held up fine. These 2" ones are rated 50lbs each. I have 4 under a lemonade stand that weighs 70lbs. Roll great.
Yes, I have 2 with and 2 matching without.
No, they are loose packaged. Nothing other than wheel assembly