It's to hold pins for dress making so they are readily available, for hemming or some such!
Thought everyone took home economics in grade 11. Great source and course for babes during high school, that and typing 11. I was the only guy in typing class, what a hoot!
Also used for construction but that would be the 'nail-o-matic, screw-o-matic, bolt-o-matic or nut-o-matic'!