stuck bolts overflow access bathtub

[wAYNE]

No good. I seemed to actually be able to start tightening the right bolt, but would not budge when loosened. Tried moving it back and forth. All the vice grips were doing was stripping the bolt further.

I guess I'm pretty much settled on the silicon adhered cover, but there's one last approach that may work IF such an adapter is available. I refer to something like these:

Notice that some of the inserts there look notched as if to be tightened by a screwdriver. Although I don't think these are right for this application, is there such an insert that is self threading? In other words, using a screwdriver, could I create the new threads on these corroded studs simply by tightening with such an insert? An alternative would be to simply epoxy a slightly larger insert over the threads and then use slightly larger cover bolts. I'm not sure what epoxy would be suitable however. I've had good luck with JB Weld for many jobs, but never anything where the exposure to moisture would be this high.

[TimR]

Every plumbing job is different and I don't mean to sound like an expert. However my experience has been if you can get it to move, even a little, tight or loose, if you continue to give it a shot of oil and wiggle it it will come eventually. Mangling the exposed threads doesn't matter, nothing you can do is going to save those bolts. You just want them out of there. If you were very patient and skilled with a small file, you might even be able to shape them into a hexagon and get them out with a socket.

If you decide it's just not worth the effort, here's another idea. Measure the bolts that hold the clamp on. Be really sure you have the size and thread pitch right, and check if they are US or metric. (Go to the big box store and try different nuts to see what size threads on. I recently bought a thread pitch gauge and am embarassed I never did it before. But really just testing it is fine.) They are probably a common size, 10-24, 1/4-20, etc. Then either buy a longer bolt or a piece of allthread and a bunch of nuts. You're going to insert the bolt or allthread through clamp into the overflow pipe, you're going to tighten down the clamp with a nut, you're going to drill two more holes in your overflow cover, and with the same bolt you're going to hold the overflow cover on with another nut outside. (if you use allthread then a castle nut is nice.)

[Thomas]

Getting late in the game but how about tiny sleeves over the studs like you use running straight copper pipe. Glued in. Shorten the studs and shorten the new screws.