The Capped Bust Dimes of 1809 to 1828 were struck on planchets from a composition of silver (89.24%) and copper (10.76%) with a weight 2.70 grams (41.67 grains). These coins have an approximate diameter of 18.8 millimeters, although slight variances are possible. All coins have a reeded edge.
The dimes produced with a modified design between 1828 and 1837 were struck on more standardized planchets, due to the use of the closed collar. The Philadelphia Mint had installed new equipment and began to employ new technology such as the closed collar. This provided for more standardized sizes, meaning the coins would no longer be having minor different sizes, as had been the case before. During this period, the diameter of the coins was 18.5 millimeters.
Initially, the coins struck with the modified design carried the same weight and composition as the prior design. However in 1837, the composition was modified to 90% silver and 10% copper, which would remain the standard for silver coinage within the United States.
taken from: http://cappedbustdime.com/