Thanks everyone for your guesses! The correct answer is a Christmas light bulb...the big old fat ones. I got the idea to make a fabric string of "lights" for a little extra holiday cheer around here this year. After a couple attempts, the prototype below is my favorite.
(I'm thinking the finished project might need a little glitter glue sparkle too.)
Of course, when I get the finished project presentable, I'll share some photos.