WordNet records no synonym and no antonym for stringer. It is the only member of each of its synsets, which is common for technical, taxonomic and single-sense vocabulary — there is no other English word that means the same thing. The broader and narrower terms below are the useful relations in that case.
Counts are distinct word forms across every sense. A synonym that appears under three senses is counted once here and shown three times below, under each sense it belongs to.
a member of a squad on a team
“a first stringer”
a worker who strings
“a stringer of beads”
brace consisting of a longitudinal member to strengthen a fuselage or hull
a long horizontal timber to connect uprights
Synonyms, antonyms and the broader and narrower relations for stringer come from Princeton University’s WordNet. Full sources and licences.