At 5.08 mm, there is enough room for 16-28 AWG wire with the rising cage clamp, and the 18 positions give you one terminal per circuit on a control or power distribution board. The green housing is polyamide (PA66), which handles the typical 13.5 A per circuit without softening at the screw clamp.
Termination and torque — the rising cage clamp detail
Wire termination is via a rising cage clamp — the screw (M3) lifts a brass, nickel-plated clamp plate that traps the conductor against the bus bar. The specified torque is 0.68 Nm (6 Lb-In). That is the setting to use on the driver; overtightening can strip the M3 thread in the PA66 housing, while undertightening leaves the wire loose under vibration. The clamp material is brass with nickel plating, and the contact surface is brass with tin plating — adequate for the 13.5 A rating in a dry indoor environment.