US sink drains only come in 2 standard sizes. A bar sink/lavatory sink is 1 1/4”, and a kitchen/laundry is 1 1/2”. Looks like you have a bar sized sink to use for a laundry sink .

The sink size is 18.5”x16” and is perfect for the laundry room. Can you suggest a drain that would work given that piece in the bottom?

Here is a picture of the sink from the top

Have you asked the place where you bought sink if they have what you need or where to buy it?

If you already have a plumber involved just let him get what he needs to plumb it in rather than trying to buy parts for him. Not a good time/place to try to save money by supplying your own parts. If it's an unusual size he may have to go back to or even into the wall to fit the appropriate adapters.

Thank you both for your advice! It tools like that small metal pipe is welded to the sink. The plumber is still trying to find a solution. I just hope that we won’t have to detach the sink and get a new one.

You have an Elkay Perfect Drain, which requires a kit for that design. Look in the sink box.

Elkay installation instructions

Ytube example

This is extremely helpful! Thank you so much, I was totally lost.

A wise person once said "after all else fails,read the instructions".

That appears to be a disposal flange.