Ƙarƙashin allura, wanda kuma aka sani da abin nadi na allura, nau'in nau'in nau'in nau'i ne na abin birgima wanda ke amfani da dogayen, siraran siliki maimakon ƙwallaye. Rollers suna da tsayi wanda yawanci ya fi girma fiye da diamita, wanda ke ba su damar tallafawa nauyin radial mafi girma fiye da bears ball. Ana yawan amfani da igiyoyin allura a aikace-aikace inda sarari ke da iyaka kuma ana buƙatar babban nauyin radial, kamar a cikin injina da na masana'antu.