It is not conserved, its sequence is not the same in all bacteria. Indeed, it has a slow rate of evolution (mutation) that make it perfect to build phylogenetic trees.
As correctly suggested by David in his comment, here are some references about the 16s rRNA and on how it is used to identify known and unknown bacteria.
http://www.sciencedirect.com/science/article/pii/S1369527499800526
http://nar.oxfordjournals.org/content/38/22/e203
https://www.ncbi.nlm.nih.gov/pubmed/18828852
https://www.ncbi.nlm.nih.gov/pubmed/27388368
https://www.ncbi.nlm.nih.gov/pubmed/27659439
https://www.ncbi.nlm.nih.gov/pubmed/18353221
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2760787/