Here are some measurements!
Davis Vertical Feed from 1899 - 8.5 inches
New Davis Vertical Feed 1919 - 8 inches
Eldredge Two Spools - 8 inches
Singer 319w - 8 inches
Rocketeer 503a - 7.25 inches
Singer 401a - 7.25 inches
Spartan - 6.25 inches
Pfaff 230 - 8 inches
Pfaff 260 - 8 inches
Pfaff 1222e - 7.75 inches
Nancy