On 8/3/2016 6:21 PM, Maurice wrote:
Previous owners had fastened down an inspection chamber lid on the patio,
but the screws will not budge.
Tried numerous applications of PlusGas, and it does disappear down the
sides of the screws, which later still refuse to move at all.

Apart from keeping on with the PlusGas, are there any other ways of
persuading the screws to turn?
(Last resort: drill them out...)

The cover and sample screw can be seen he

https://dl.dropboxusercontent.com/u/...tion-cover.JPG

https://dl.dropboxusercontent.com/u/...over-screw.JPG

I had the same problem with a cast alloy cover on a round plastic
inspection chamber. Possible galvanic corrosion between the steel screw,
alloy cover, brass insert, in that particular case.

I drilled them out.