This is the later style bolt for the slightly improved Model 56 or Type II Madsen clam shell SMG. This bolt has reduced side contact which serves to decrease friction and lighten the bolt, both adding up to a somewhat faster rate of fire. Since it also used a double column double feed magazine it is also easier to load. Some people have had luck using this bolt in earlier guns as the actual size is the same. Not so sure it is a good idea.
