From 1946 to 1964, the Roosevelt Dime was struck in a composition of 90% silver and 10% copper. These coins have a standard weight of 2.50 grams and diameter of 17.9 mm with a reeded edge. During this time period, the mint mark for dimes struck at the Denver and San Francisco mint facilities appears on the reverse of the coin to the left of the base of the torch.
Starting in 1965, the silver content was removed from circulating coins resulting in a significant composition change. The dime was struck in a new copper-nickel clad composition, consisting of an inner core of pure copper and an outer layer of copper-nickel. This combination yields a net composition of 91.67% copper and 8.33% nickel with a weight of 2.27 grams.
For the first three years of the clad composition, mint marks were not used to prevent hoarding. Mint mark usage resumed in 1968, but the placement was changed to the obverse, located between the truncation of Roosevelt’s neck and the date. The Philadelphia Mint started using the “P” mint mark on the denomination in 1980.