Advice on (square-to-round) manhole covers?

[Fez111]

Hi all,

Replacing an existing patio with new porcelain tiles. Currently have a plastic round manhole cover which has 500mm diameter lid (opening inside is 480mm). I want to replace this with a square recessed manhole cover to hold the tiles.

The issue is, all the square-to-round recessed covers i can find online seem to have much smaller openings/ diameter for the circular bit underneath (220, 350, 450, etc). So am i missing something completely? or does it not make a difference if the circular opening attached to the bottom of the square to round recessed cover is say 450mm? as long as smaller than current opening?

Thanks in advance

 

[Stivino]

There is an inbuilt safety feature with round manholes, it's impossible for the cover to fall into the hole.

 

[jj4091]

As long as your new cover is larger than the diameter of the old one it shouldn't matter. I presume you are talking about the lift out type of recessed tray.