Hope RX4 Caliper Has now been discontinued and replaced by the RX4+ You can find these listings here -
Standatd - https://www.evocycles.co.uk/hope-rx4-caliper-complete-fm-std-dot-blue/mpn:HBSPC71B_z/
+20mm - https://www.evocycles.co.uk/hope-rx4-caliper-complete-fm-20/mpn:HBSPC74B_z/
Compatible With -
Dura Ace Di2 R9170
Dura Ace R9120
Ultegra Di2 R8070
Ultegra R8020
105 R7020 Not currently compatible:
Di2 R785 GRX RX815 Di2
RS685 GRX RX817 Di2
GRX RX810
GRX RX600
GRX RX400
Super Record
Record
Campagnolo H11
Sram Red eTap AXS
Sram Red
Sram Force eTap AXS
Sram Rival
Sram Apex