After posting this in the wrong forum here it is again:

I am about to become the proud owner of a Speed Graphic. I understand that this camera will only take filmholders for graflok backs. Which leads me to my question: how can I differentiate between a graflok and a graflex filmholder? Is there an easy way to spot the differences from sight, say an ebay picture of a back?

Congratulations on the Speed! What great cameras...

What you want to do is read all the info on this site. It's amazing how many of your questions will be answered here and on the forums. A good explanation of the backs is found here:
http://graflex.org/speed-graphic/features.html#GraflokBack

The Graflok is also known as the Universal back. It can use any modern film holder and most roll film holders. If you buy new, it will fit. If you buy used, just make sure it's NOT for the Graflex back, although Graflex holders are hard to find...

It's very difficult to spot the difference in a holder from an auction picture. The Graflex holders are just slightly larger (1/4 inch I think) and have grooves on the long sides.

I may be wrong, but if you buy plastic holders, they should fit. I don't think the newer plastic models ever were made for the Graflex back? Other can correct me, and add info on spotting the difference...

Good luck with your Speed!

I have never seen plastic film holders for the Graflex back, so any of the modern plastic holders will do just fine. If you purchase any of the older wood film holders, be sure, no matter whether they be Lisco, Fidelity or whatever, they are labeled "Graphic". That tells the difference between the standard holders and the larger grooved holders for the Graflex back. Your Graflok back will also accept most roll film holders which are installed by pressing down on the focus panel spring arms and removing the panel. The roll holders are held in place by the sliders on the back. Good luck with your new camera. I think you will enjoy it a lot.

Thank you for the replies. I can't wait to try out the camera.