Trek 1500 slr Headset size

Bozman
Bozman Posts: 2,518
edited July 2011 in Workshop
We're building a winter bike for a mate and we're after a headset for a Trek 1500 slr(roughly 2006), does anybody out there know the size of the headset, apparently it's a "Aheadset w/semi-cartridge bearings, semi-integrated, sealed headset".
Cheers