From Cocoknits -- 
"I have long wanted a tiny needle gauge tool for travel-knitting. The big squares or rectangles are okay for at-home knitting, but clumsy for travel - so I fashioned one based on those a jeweler would use to size diamonds. 
The result is a joyous rainbow stack of connected discs for identifying knitting needle sizes US 0-15 / 2-10 mm. 
And because Cocoknits is committed to avoiding plastic wherever possible, we manufactured it from PLA, a 100% biodegradable, plant-based plastic substitute!"