There are three threaded plugs on the older type front hubs, a small one at the bottom for draining the hub, a big one at the top with a 1/2" square drive head for filling it and a third 1/4" head plug about two thirds of the way up on the front for guaging the level - oil flows out when it's full enough. The hub takes 1/2 imperial pint (8 fl oz) EP90 gear oil.
On the later hubs there is no level guage plug, these hubs should instead be filled with the new grease packs.
You can use the grease packs in the older type of hub, but then you should mark the filler plug with yellow paint as a code to tell the next guy along that's what you've done.