Just in case anyone ever wants to run a Giant OD2 fork you will need to buy the OD2 MTB headset in order to get the upper race for the 1 1/4th upper end (which I'm pretty sure is, in fact, an FSA 51), which will fit into a standard 44mm head tube:
Then use whatever your favourite brand of 44mm/external bottom cup for the 1.5" end.
Just in case anyone ever wants to run a Giant OD2 fork you will need to buy the OD2 MTB headset in order to get the upper race for the 1 1/4th upper end (which I'm pretty sure is, in fact, an FSA 51), which will fit into a standard 44mm head tube:
Then use whatever your favourite brand of 44mm/external bottom cup for the 1.5" end.