Thread Size of Spikes for Revel F206

Was hoping that someone might know the thread size for the floor spikes. Bought a pair of used F206s that came without the floor spikes. I am looking to put on a pair of outriggers and need to find the right size bolt.

I found somewhere on internet that it was 1/4"-20 but this is way too small. A 5/16"-16 is close. I can get a couple of threads on and then it binds up.

Any help would be appreciated !
Sounds metric, call Revel. I have F32's and they are 1/4 x20, so they may have changed insert suppliers with the new series.
How do you like them so far? I heard them at RMAF last year but the local dealer doesn't stock or have a showroom. I had thought about upgrading but can't get to demo them. The reviews sound like vast improvements of mine.
If all else fails, go to a store like Home Depot and buy a few different threaded bolts that look about the right size. Try them one by one and see which one works. Also, make sure you get both metric and sae bolts.
Do you mean 5/16 -18?
5/16ths comes in two thread patterns. 18 or 24 threads per inch. Try the 24 thread count in the 5/16 size.
Thanks for your replies everyone. Sorry, I did mean 5/16-18.

After a few trips to home depot I figured out the correct size. It is indeed metric !

For anyone that comes across this problem in the future the hex bolt is 8mm diameter with 1.25 thread size (M8-1.25)

Theo: I like the Revels quite a bit but don't have a lot of experience with different speakers or the previous Revel Performa series. I bought them based on reviews alone and have not been disappointed.
What outriggers are you getting? I was thinking of getting the 206's myself.
Cobes, thank you for your response. I would agree that if they are reviewed to sound better than the previous models, I couldn't go wrong. I am hoping there will be some on display at RMAF this year.