Speedo Drive on Disc Fork

[AgentX]

Hi everyone-

I'm putting a new disc front end on an old bike.  Can anyone help me by measuring the size of the hole in their speedo drive?

My drive is a metal-bodied one drilled to fit the narrower old-school axle, so I'll need to bore it out.  It won't fit over the new-style axle, and I can't tell what the diameter should be since I don't know where on the axle it needs to rest when assembled.  (It has two diameters plus a short, tapered transition between them...)