The HB-RE124 is the special steel bearing cup used on all Campagnolo and Fulcrum hub with;
1) a 17mm diameter alloy axle same cup has been in use since 1999 for these type of hubs (except 2015 onward bora/zero front rim brake wheels). Gits disc brake wheels too.
2) "cup and cone" steel bearings
The hubs with USB or CULT bearings use a cone of the same shape but a harder steel.
Simply remove the old cup and press in the new one. Cyclus make the correct tool for the job. If you love the perfect tools just ask and I will supply this for you.