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Ti-Cycles hose coupler"
The above comes with some unspecified barb size. Just be certain to use the correct size barb for the ID of the hose type used as there is no "one-size" barb for all Shimano hose versions. For example, BH59 (comes with rs785 set) hose is 2.3mm ID; BH90 (stiffer) is 2.1mm ID. I am now using the BH90 and like the firmer feel.
Since the product indicates it uses a "standard compression nut" I would try using OEM Shimano barbs and olives in this coupler, as these parts are readily available and known to be hose model specific. The correct Shimano barb for BH90 is silver color, whereas the BH59 is gold (brass).