The acronym SAPI is a military term. It means Small Arms Protective Inserts. These inserts are small plates that are used in body armor to protect against heavy duty artillery.

The Japanese did insert bamboo into the arms of the POWs and they would also jam sharp bamboo sticks under their fingernails.

those manufacturing small arms are classified in SIC 3484: Small Arms.

small arms

those manufacturing small arms ammunition are classified in SIC 3482: Small Arms Ammunition