Double row. Rolling pin is a massage tool specially used for health care. Made of high quality materials, it is fashionable in appearance and convenient to use. "Single row of steel bars" means that only one cross bar is used to fix steel bars; In the double row, there are two cross bars to fix different levels of bars respectively. Double-row rolling pins are more flexible than single-row rolling pins, and can be used in different angles and positions by adjusting the distance or angle between two cross bars, with wide stress area. So double-row rolling pins are better.