Ptg that measures all surfaces

which ptg's (if any) measures all surfaces metals, platics etc or do you need to have two separate ones for each surface? thanks

 

You'll need two. One for ferrous and non ferrous and a seperate one for carbon fibre etc.

 

You'll need an ultrasonic gauge. Not only are they expensive, they're not very accurate (you'll notice the companies that make them don't actually market them for automotive use because they're way out of spec to be used for this reason.
Lowest priced ultrasonic thickness gauges are around $1000-1100.

I actually did some further explaining information on these tools on an autopia post not too long ago:

Which Paint Depth Gauge? - Page 5 - Autopia.org