I was betting on the association with the D-Rings.
But check out #00706 ----------
Snap Hooks for Rifle Scabbard
http://www.hayesotoupalik.com/U.S. Cavalry Equipment.htm
Man that's it! Thank you very much! Nice research.
US Army WW1 Set of Two Snap Hooks for use with M1903 and/or M1 Garand leather Scabbard Straps