This (1975-1978) Jefferson nickel which is struck on a 4-sided aluminum Philippine 1 Sentimo planchet, and has a weight of 1.2 grams, which is about 75% lighter than a normal nickel.

Probably, this coin is from 1976 since the other known examples of 5c on this type of planchet are, to my knowledge, all dated 1976. There are around 6-8 known.

NGC MS-61