Need help with a drain size

[Nathank]

Recently moved into my house and the bathtub drain looks awful there's a leak in the tub faucet which has subsequently damaged the area around the drain. For some reason the drain is not wide enough to sit flush with the tub. The flange is the correct size but it allows water to sit all the way around the drain cap which has rusted and damaged the tub. I've already tried replacing the drain cap but it's the same size. My question is how I can get this sorted so I don't have to dry up the water every time the faucet gets used. The diameter of the section is 3 and a half inches. Attached are pictures of the drain for reference.


http://m.imgur.com/Lr3N5UD,0kvXbLQ

 

[Terry]

You may be able to paint or refinish the tub there. That also may not be the only rust you have. I've pulled some tubs with hidden rust too.