18 gauge sterling silver filled full hard round wire. Polished shell is the operculum of a seashell. The operculum is like a foot and serves as a sort of trapdoor to close the mouth of the shell when the soft part of the animal is retracted. It is found on beaches throughout the pacific, no live shell are used to make them 

round shape  -  3/4"dia     
square shape  -   1/2"x1/2"  
rectangle shape  - 1/2x 3/8"

Available in 7" to 8.5" circumference sizes. 

Note: Our bangles do not have an opening,  so what is most important is that the bangle you order slides over your hand.
The best way to determine this is measure inside circumference of a bangle you already own and is comfortable sliding over your hand.
If you don’t have one, you will need to measure your hand circumference. Use a tape measure if you have one or you can take a strip of paper and wrap it around your hand mark the spot where the paper meet, then measure with a ruler.
Also note: the wrist is smaller than the hand so measuring your wrist and using this measurement to size a bangle will be to small.

Made in Hawaii