Joined: Oct 2018
Posts: 2,182
Likes: 1,055
From: Columbus, OH
Bikes: Pake C'Mute Touring/Commuter Build, 1989 Kona Cinder Cone, 1995 Trek 5200, 1973 Raleigh Super Course FG, 1969 Raleigh Superbe, 1986 Miyata Nine : 1960/61 Montgomery Ward Hawthorne "thrift" 3 speed, by Hercules (sold), 1966 Schwinn Deluxe Racer (sold)
I'm not sure this is something you need to specify to your frame builder. Many forks, threaded and threadless, come with such braze ons without knowledge of which rack can be bolted on there.
Many racks and lowriders are also adjustable for different fork configurations. Tubus racks are the easiest example, but Surly and Blackburn also sell racks. You must like this fork to pay to alter it.