1set Stainless Steel Bathroom Hot and Cold Tap Faucet Lock Nut Hex Brass Female Locknut for Secure Faucet Plumbing Installation, Nut ID 30.5mm, Metal Washer ID 32.9mm, Rubber Washer ID 34mm

$7 on Amazon But I fully support the just-print-your-own here. Plastic is fine for this application and ready in one hour Vs hours of driving around and buying the wrong part three times is a win.