Both sides have a 16 mm attachment. Used to connect two units with 16 mm spigot, or to obtain a 16 mm female attachment from 16 mm spigot.
Manfrotto
Double 5/8″ Female Adapter
It converts 5/8″ (16 mm) stud to a 5/8” socket
Multiple usage
Easy to mount
6,5cm in height
15,00€ (ex. VAT)