When the two key halves come together, they create a heart on the end which is used to turn the pin. This is a piece intended for lovers, the keys can be worn as pendants and symbols of the two halves of one heart.
The medium size cuff (pictured above) inner diameter is 2.45". The opening is 2.1" wide
The links to the three other components to complete this assembly are as follows
love bangle pin (medium)
Heart key female
Heart key male
Link to hi-res images here
Link to all sizes here