What is that rubber cord that go around a blind call?

How do I grasp efflorescence rotten of my...
Answers:    Well everyone said "spline" and I concur. I will add that if you are replacing one, buy the tool :-) Its merely a few bucks and makes an "interesting" errand very comfortable
4 prong outlet?
spline
http://www.acehardware.com/product/index...