The United States Three Cent piece was issued in two separate metal compositions. From 1851-1867 the Three Cent piece was made of 75% Silver. The silver version is also commonly referred to as Trimes. There were a great many of these later dates 1863-1872 that were melted by the US mint in 1873. This act of mass destruction has created some very hard to find later date coins.
The Nickel three-cent piece was produced from 1865-1889. The metallic composition of the coin was changed due to the fact that the public was hoarding silver at this time and there was simply not enough to go around.