Pestles are most commonly used in conjunction with mortars, though thinner, disposable models can be used with centrifuge tubes to resuspend bacterial cells, precipitates of nucleic acids, or proteins and pellets of other materials. With mortars, pestles are typically heavy tools with a rounded end for crushing and grinding samples. They are integral parts of the grinding process when operated by hand, and their use is straightforward and simple, with extremely low maintenance.