There is no difference in the form factor between a thin and a Zero client. Generally, these are small devices that weigh a couple of pounds. They are fanless and very quiet. Typically they can be mounted on the back of a monitor to avoid crowding the desk space. Zero clients can also take the form factor of laptops or All-in-One devices (monitor with PC combined). Even former PCs can be made into Zero clients. It really comes down to the operating system that is running on the device of choice. Depending on the device, there will also be varying peripheral options (USB, COM port, wifi, RJ 45, HDMI, Display Port, etc…).