Braided Hair Cents were struck out of pure copper, which was also the reason for the discontinuation of the series. Copper had risen in price steadily since the early 19th century, and by 1857 it had become too expensive to profitably mint large cents. These pieces weigh 10.89 grams (168 grains) and have a diameter of 27 millimeter with a plain edge.
All were minted in large qualities at the Philadelphia Mint, as the branch Mints did not strike minor (copper) coinage until the early 20th century. The coins do not carry a mint mark.
A complete set of coins from 1839 to 1857 is usually considered to be easy to complete when collecting by date only, but finding choice examples with no corrosion or other visible problems visible take some time for many dates.
taken from: http://braidedhaircent.com/