Off-White/Ecru River Shell 2-Hole Button 11mm / 7/16", Pack of 95-100 # LP-79
Slightly warm off-white, not as warm as what we call ivory. They are about 1/16" thick and the holes are 1.5mm. Most are a bit iridescent, at least on one side. (Clearly these are not plastic buttons!) Satiny, thick for their tiny size, durable, smooth and a bit shiny. None are grayish; that's a lighting/camera issue with the iridescence. Most of the backs are the same; some may have a spot of seashell peach tone. You'll get at least 95 buttons, for $7.25.
They're between 10.5 and 11mm, just shy of 7/16" and definitely larger than 3/8".