1/4" plywood thickness for shaper cutter

[Bill Dufour]

I am thinking about getting a new set of knives for my shaper to do rail and stile casework. I know construction plywood has changed over the last few years and gotten thinner. So if I want to use 1/4" plywood how thick is that these days. Is it all metric now? what thickness groover do you recommend. When I made my milling machine cabinet I had to raise the edges of the plywood to fit.
I see identical sets sold with either 1/4" or 5.5mm? panel thickness I have no idea which is better and likely to stay useful in the future. For solid wood it does not matter as I can plane or bevel the edges to fit.
The big box stores Label their ply in a weird system rather then metric they use fraction of say #/132's which just confuse the issue.
Bill D

[Ken Combs]

Not a direct answer, but I always order MDF w/hardwood veneer for stile and rail cab doors. Because it is actual dimension. I use mostly 1/4 for most doors.

1/4" Ply core is almost always 7/32". All others are normally 1/32 under the nominal also, at least locally. So the label at the big box store is actually correct.

With imported products the measurement varies by source country in my experience. 5.5 and 6mm are common.

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[Wayne Lomman]

I don't rely on ply thickness but rather set up to suit what actually gets delivered. Sometimes this means more than one run through the spindle moulder. If you want reliable size, Ken is right - use mdf products. Cheers