A hairbrush (also spelled hair brush) is not only good for brushing the hair, but also popular as a spanking implement.
The bottom is spanked with the flat or slightly rounded back of the hairbrush, which should be even and smooth. Traditionally, wooden hairbrushes are used for spanking; however these days often a plastic one will have to do (though these are far less 'effective'). The hairbrush is similar to the following implements: bath brush, clothes brush, wooden paddle, and wooden spoon.
For variation, also the bristled side of a brush can be used for spanking. If the bristles are stiff, they will leave a dotted pattern on the skin, but they can also pierce and break the skin, a type of injury that is better avoided and is considered unsafe play. This also especially applies to brushes with metal bristles (with plastic tips).
For further variation, the brush can be used in pauses of a spanking session to brush over the skin, which greatly sensitizes the nerves.
From the series "After Curfew" by Salalo (2013).