For a 6mm bolt, 9mm (11/32" approx.) depth should be sufficient.
Just take some pre-measurements and make sure your're not going too deep to damage anything.
After going thru a couple "mount finder" exercises on Sanus and Samsung's websites, I decided to mount my LN32A450 with a Sanus VMPL50 mount. Last night I placed the brackets on the rear of the television and thought I'd bought a mount that was too large ... until I figured out that the spacers were for this purpose.
My question was whether others have 2nd guessed using the M6 x 35mm (the longer bolts) with the spacers (for any brand mount). It just seems like there's not enough of a thread going into the TV ...

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