1 1/4" is the usual size. Your's looks like that.

It's the right size. Just maybe defective in production, like it has a burr or something on it. Is it a china sink mounted to solid surface? Or is it solid surface? If it's the former, return it. Trying to fix it will probably break it. If it's the latter, then some sandpaper might fix the burr if it's not too bad.

Appears to be all solid surface. White area is same material as countertop. Drain hole appears to be 1 1/2..Delta part 1 5/8. Is there a way to successfully enlarge drain hole?...Thx!

The sink is defective. Notice the little burr at 8 o'clock.

Got a 1 1/4 inch pop up drain assembly. This solved the problem. Who knew they came in different sizes...Thanks for all info & suggestions!

I want konw how to make wood sink .how to making hole siz and please advice me

If please give me engineerin drowning