I had to replace 2 manhole covers in my back garden as the existing ones were rusting away (including the frames). Unfortunately I only measured one, because after replacing the first with no problem I discovered the second was slightly bigger, in fact about 10mm bigger all round than the 600x450mm frame and cover I bought. This means that the frame overhangs the edge of the brickwork which, although the manholes are in the corner of the garden and not regularly trodden on, doesn't seem safe to me. Anyone got any idea how to shrink the manhole slightly, short of rebuilding it? I'm hoping some sort of liner could be bought or constructed maybe?