I don’t know about others but here there are Floor Grates made from stamped metal that are painful to step on but not able to hold the weight of a person plus power chair and by brilliant design, they are placed in the natural path where folks have to walk or in my case ride a power chair so if the chair hit one already damaged it would fall into the hole and have a hard time even getting out.
I had built one of these before and it was getting rickety with two layers of 1/4 in plywood, but trying to move a refrigerator over it totally did it in,
So now I am building another with 3 layers and hope it holds up.
So I guess it is only the standard size here but in case anyone else has that standard. or if they can rescale it to their needs here is the design.
the small one I made twice this time, but it only sticks up one layer.