Use a bigger one than the tile insert, 100mm.
90mm is not a DWV standard size.
With the current COVID lockdowns, I cant easily waltz into a store and figure out what I need, so I am left with online shopping... which doesn't always work out.
I bought a tile insert grate (from an Australian online store). The outlet diameter is just under 90mm. I do not see any 90mm puddle flanges on the market. I bought an 80mm puddle flange just to look at dimensions. (For $3 from Bunnings, not much to lose! Not sure how they can sell them so cheap.)
Anyway, as can be seen from images, doesn't work. Grate diameter for an 80mm puddle flange is........ wait for it....... 80mm. I can't find an 90mm puddle flange to purchase. All are 100mm, 80mm, or smaller.
Have I bought a unique grate here or am I missing something fundamental?
*sigh* Amazing the details that can hold you up from getting on with it.
I'm no expert, but know enough to be dangerous...
__________________
Use a bigger one than the tile insert, 100mm.
90mm is not a DWV standard size.
I may be asking obvious questions here, but if I buy a 100mm puddle flange, the grate obviously won't sit on it/make contact with it. This means that the only thing supporting the grate will be the screed. Even then, it will only be on the corners of the grate as the screed will obviously finish outside of the drain pipe and so minimal screed supporting it.
I think I may need to buy a different grate? Question I have is, why would an Australia bathroom place sell a non standard tile insert grate? The box even says "complies with Australian plumbing codes" so some consideration has been given for the Australian market.
I'm no expert, but know enough to be dangerous...
__________________
The tile insert is not supposed to be a tight fit to the puddle flange, the tile insert is to give the cosmetic finish to the floor and be above the puddle flange, the size of the waste pipe is relevant to the plumbing size. The puddle flange on the other hand is to allow water under the tile to drain to the waste, if the tile insert is a perfect fit then there will be no way for the under tile water to drain.