Originally Posted by
unterhausen
I don't think I have ever seen a track dropout with sockets. The problem with sockets is that the dropouts have to have the same angles as your frame, tabbed dropouts can be made to fit almost any angle.
Nagasawa made socketed track dropouts. The seat stay socket was a separate piece to allow angle adjustment for different frame sizes:
Those ones were from the mid-80s; not sure if they're still available.