It's already been roughly explained in pieces, but here's the whole of it:

M8 is the diameter of the stem, and the 1/2" Chris specified is the length. In Metric, you'll want M8-15mm as others have said, as that's the other common size along with M8-25.

The 1.5" or 2" (or 3" or 4", etc) refers to the diameter of the wheels.

Swivel means they will rotate 360 degrees without restriction.

I prefer "dual locking" or "total locking" casters whenever I can, which means when you push down the locking lever it stops the caster wheel from spinning, as well as the caster itself from rotating. It helps make things a lot more solid and less wobbly.

Here's one example that I believe someone else had shared that they used with theirs
https://www.amazon.com/Standing-Wheels-Polyurethane-Casters-Capacity/dp/B0894RKS3G

https://www.amazon.com/Standing-Wheels-Polyurethane-Casters-Capacity/dp/B0894RKS3G

Thank you so much for sharing this! I just ordered Apex 3 leg and am trying to order caster wheels. I tried to search tips on it and ended up this thread. Do you think I can order the same size of caster wheels for Apex as recommended for Apex Pro Max? Apologies if this is a wrong place to ask this question!

Thanks for that tip, I hadn't thought about it, I planned to setup the piano next to my computer anyways so that will make things easier.

I have a Yeticaster mic set (that one has some settings to record music) and a Logitech C922 camera with all the setup for recordings (I use it for some interviews in podcasts and videos for the proposals I do for high end clients), I also have an Aimezo 3 Desk with Heavy Duty Wheels so I can move everything I need easily for any recording needs.

I also have a DIY solution for sound acoustic panels to avoid echo, so I'm ready to record anything I need with good sound quality :D

By the way, I found a store that sells the Yamaha P125 with full stand and 3 pedals at $1114 USD, I'll call them tomorrow to make sure they still have it as it's usual that people here don't update their online inventory and I'll call other stores to see if they have it a bit cheaper.

Thanks for everything one more time :D

I have casters on mine. Specifically these ones:

https://www.amazon.com/Standing-Wheels-Polyurethane-Casters-Capacity/dp/B0894RKS3G

Works very well so far.

No regrets on the Apex Pro. I'm using a Sparrow Peak espresso top, 72x39 cut down to 65x39. I went with the 31.5" feet for the pro for stability.

If I push back and forth on the desk fast the outer 2 monitors will shake a little, but stop but dampen in under 3 seconds (you're never going to avoid that with any single beam triple mount). The outers are on standard swivel monitor arms so that may be why, but they definitely don't shake as much as when I had a lighter desk and 3 single monitor arms. If I take my fists and pound the desk a few times, no shaking in the outer monitors.

My desk is on carpet and I did add casters which also don't cause any issues (but do allow me to roll this 275+ lb setup away from the wall to work on the back if needed).

https://www.amazon.com/dp/B0894RKS3G

BTW: lock the casters to install, the lock locks the wheel from rotating, but also locks the swivel above the wheel so it can't spin around, makes screwing it in a breeze.

I don't even lock my wheels now that it's in place, the desk is so heavy it's not moving on the carpet.

Also, the EMMA monitor mount is HEAVY, it's a standing desk leg flipped upside down with t-slot channel as the beam and 2 double articulating monitor arms for the outers.