Earlier here I think the crescent tiara and circles necklace have been mixed up. Since the QD these are now known as the Duchess of Teck's Tiara and a diamond hoop necklace.
I cannot recall ever seeing Princess Margaret wearing the Duchess of Teck's Tiara.
Note the tiara of crescents and necklace of hoops.
--Previous Message-- : Princess Margaret often wore the circles : necklace, but not as a tiara. The Queen : Mother had worn it once as a tiara. I : believe Princess Margaret wore the crescents : as a tiara. :