stopper
n.— «Unlike many other public and private parks, Washington Square’s new granite benches do not have skate deterrents, or “stoppers”—small metal ribs attached to the stone that prevent what are known as “grinds,” in which skateboarders scrape their metal axles along a smooth, hard surface. Since the stoppers were introduced in 1998, hundreds of millions of them have been added or retrofitted onto new benches and hand railings around the country.» —“For skateboarders, it’s not the same old grind in new park” by Will Glovinksy The Villager (New York City) Sept. 2, 2009. (source: Double-Tongued Dictionary)