zaa Bathtub Drain Hair Catcher, Silicone Collapsible 1 Pack Drain Protector for Pop-Up and Regular Drains of Shower, Bathtub, Tub, Bathroom, Sink

Q: What is the internal diameter? Will it cover my 3inch pop-up drain?

Yes. I just measured my tub pop up drain and it is also 3 inches. The narrowest internal part of this gadget is 2.5 inches but because it folds flatter into itself, the maximum diameter is 4.5 inches. I saw this at my son's home and it's the best thing since sliced bread!