Thanks and yes I know about the standard length of the M8 screws. The Monoprice wall mount model 8588 that I bought for my PN60F8500 came with M8 16mm (not a typo) and M8 40mm screws and it can handle TVs up to 60" weighing up to 175 pounds. The M8 16mm screws work fine but they seem too short given the weight of the TV. The 40mm screws require the use of spacers which I didn't want to use so I was considering buying M8 25mm screws and I'm hoping they'll be short enough so that they won't go into the TV more than 21.7mm when you factor in the thickness of the wall mount brackets that attach to the back of the TV plus the washers between the screws, the brackets and the TV. However I'd like confirmation that the service manual actually says that the M8 screw length should be between 20.7 and 21.7mm like the Samsung chat rep told me.I have no experience with wall mounting, but you will not find any M8 screw with such a certain length of 20,7 or 21,7... they have 20, 25, 30, 40 etc.
But for such a large tv, 20mm seems very short.. This is a 30kg plasma, and samsung uses for their larger tvs sets screws longer then 40mm..
It is really strange that there is nothing in the manual.. I think the reason is because Samsung sells their own wall mount kit for this plasma..
I agree that it's strange there's nothing in the manual. Here's a link to the page from the manual which indicates the M8 screws but no length details. The manual on the Samsung support page for this TV is a generic e-manual for multiple models and this link is the specific one for the PN51F8500 and PN60F8500.
Btw I found it ridiculous that the Samsung chat rep told me to buy the service manual in order for me to see this information in writing when it should have been included in the user manual in the first place.
Here's a link to the Monoprice wall mount user manual as well for reference.