South bend milling machine spindles do not have a drawbar.
Instead, the 30taper tooling is retained by a setscrew on
each side, through the keys.  This was referred to as "30 MM"
taper tooling.  It is essentially obsolete, and the collets
for the original chuck are scarce.  An ER40 (or 30) collet 
chuck with an integral NMTB 30 taper can be easily modified
to fit a SB spindle merely by milling the necessay setscrew
pads into each side, centered on the key drive slots.