The 387217303: Top termination uses screws with a captive plate — the plate stays captured under the screw head, so it won't drop out during field wiring. The bottom termination is a 0.187" quick-connect tab, insulated, for pre-made harness leads or spade terminals. Wire range is 12-22 AWG, covering common power and control circuit sizes. The terminal screw is steel with a zinc clear chromate finish.
Against the 2-circuit 387217302 at the same 0.375" pitch, this 3-circuit block adds one position for a third wire entry — the footprint grows by one pitch increment, so a panel cutout or DIN-rail adapter designed for the 2-circuit version won't directly accept this one without extra space. Against the 387216703 (also 3-circuit, same pitch), the key difference is top termination: 387217303 uses screws with a captive plate, while 387216703 uses plain screws. The captive plate holds the wire without the screw tip digging into the conductor — a practical advantage in high-vibration or repeated-termination service. The 387216703 is also rated 15 A vs this unit's 20 A, so the captive-plate version carries more headroom.