Can someone tell me what this thread is called?

[Jim]

I'm looking to buy some string/thread (about 5m), you know you can get
lanyards that fit to your phone or camera and normally have a tiny bit
of dtring on them something like this

http://www.pulse72geocaching.co.uk/ekmps/shops/pulse72geo/images/geocaching-lanyard-[4]-931-p.jpg

or

https://tinyurl.com/yb68s4gq

It's not the green bit i want but the tiny thread that goes through your
phone or camera, does anyone know what it's called i have looked for
strong thin nylon thread etc on google but nothing stands out.

I was wondering if anyone here could shed some light on it for me

TIA

Jim