On Sat, 04 Jul 2009 19:33:15 GMT, "Phil L"
wrote:



Why do they have to be steel? - plastic covers are available in many sizes,
and concrete slabs in many more.


Steel isn't essential, if plastic (or even concrete) is available in
the size that I'm after and will fit my existing single seal frame
then that's fine. Trouble is that I have yet to find any in the
required size in those materials either.