5.56, threaded 1/2x28, this was a replacement that Silencerco sent me but I'd already gotten another. These are $92 from Silencerco. I don't have the package but it is brand-new. If you haven't seen one of these, your eyes are not playing tricks on you-all three prongs are different heights. This is a QD mount for the Omega, Hybrid, Specwar, and Saker suppressors.
$60 shipped to you or FTF in Lubbock. Paypal(gift), MO or Check.Product Link