This handlebar fits around the seat post of an eZee Expedir electric cargo bicycle(28.6mm outer diameter) providing grips for your first passenger to hang on to. The handlebar itself is a standard clamp diameter (25.4mm) so if you need to you can interchange it with different handlebars to get the shape and size to suit you.
Generally speaking this is what is used when a child grows out of their baby capsule at around 5 years old and you still want them on the back of your long-tail cargo bike.
This handlebar is usually purchased in conjunction with the pillion seat (cushion). For a second passenger consider the Expedir Child Seat for 5-10 year olds.