Joined: Jul 2015
Posts: 7,154
Likes: 3,101
From: NW Oregon
Bikes: 1982 Trek 930R Custom, '91 Diamondback Ascent w/ XT, XTR updates, Fuji Team Pro CF road flyer, Specialized Sirrus Gravel Convert, '09 Comencal Meta 5.5 XC, '02 Marin MBX500, '84 Gitane Criterium bike
The "flat" part of the bearing cage goes towards the INNER bearing race... the balls exposed to the outside go towards the OUTER race/cup.
typically, the bottom bearing goes onto the fork with the flat side down... top bearing goes on with the flat side up.... there ARE headsets that require you to install the top bearing with the flat side DOWN, but those are pretty rare...