This is a new/ old stock, ABB RXMS1 RK 216 265-AP Auxiliary High Speed Tripping Relay 125 Volt, Combiflex Mounting.

Type RXMS 1 is particularly suitable as tripping relay due to its extremely short operate time. A special variant, which is not influenced by capacitive discharges at earth fault and which also has improved insulation across open contact, is available for heavy applications where high disturbance immunity is required. RXMS 1, in combination with heavy-duty relays, is used in high speed tripping assemblies as accessories to protection relays.