Sexy Lisner 16″-18″ Multi-Chain Necklace w Bullet Stations & 3″ Extender
Lisner went out of biz between 1979 and 1985 (accounts vary), and I think this necklace is probably from the 1970s. Using the full length of the extender, the necklace is 16″ (shortest chain) to 18″ (longest chain).