The two most obvious differences on 1804 Half Cents relate to the 4 of the date. On some coins the horizontal crossbar of the 4 ends with a vertical crosslet; on others the 4 has no crosslet. The Plain 4 is slightly more common than the Crosslet 4.
The Plain 4 obverse is combined with two different reverse types: Stems at the base of the wreath and No Stems at the base of the wreath.
Only one die variety (Cohen 11) qualifies as the Plain 4, Stems variety.
Uncirculated examples of the 1804 Plain 4, Stems Half Cent are very rare, especially with even a trace of original red color. Low-end circulated examples can be found without too much difficulty, but high-end AU examples are quite scarce.