▁dis m ant le , ▁was ted ▁power ▁through ▁fr iction ▁and ▁they ▁had ▁a ▁t endency ▁to ▁over he at . ▁The ▁thrust ▁box ▁was ▁built ▁of ▁a ▁box - like ▁cast ▁iron ▁housing ▁with ▁a ▁radial ▁bearing ▁at ▁each ▁end ▁and ▁a ▁number ▁of ▁coll ars ▁formed ▁on ▁the ▁sh aft ▁between ▁them . ▁This ▁sh aft ▁was ▁often ▁a ▁short ▁section ▁of ▁remov able ▁sh aft ▁called ▁the ▁thrust ▁sh aft , ▁linking ▁the ▁engine ▁ahead ▁to ▁the ▁prop eller ▁sh aft ▁ast ern . ▁A ▁series ▁of ▁iron ▁horses ho e - sh aped ▁coll ars ▁fitted ▁over ▁the ▁small ▁diameter ▁of ▁the ▁sh aft ▁and ▁bore ▁against ▁the ▁forward ▁face ▁of ▁the ▁sh aft ' s ▁coll ars . ▁Each ▁horses ho e ▁was ▁faced ▁with ▁a ▁low - fr iction ▁pad ▁of ▁b abb itt ▁metal . ▁Lub ric ation ▁was ▁by ▁an ▁oil ▁bath ▁in ▁the ▁box ▁and ▁a ▁pl ent iful ▁volume ▁was ▁important ▁for ▁cool ing ▁purposes ▁too . ▁ ▁Although ▁l ign um ▁vita e ▁wood ▁was ▁used ▁for ▁the ▁radial ▁st ave ▁bear ings ▁in ▁the ▁stuff ing ▁box , ▁co o led ▁directly ▁by ▁se aw ater ▁itself , ▁this ▁material ▁wasn ' t ▁capable ▁of ▁with standing ▁the ▁force ▁needed ▁for ▁the ▁thrust ▁blocks ▁of ▁any ▁but ▁the ▁earliest ▁sc rew ▁vessels . ▁ ▁Each ▁horses ho e ▁was ▁independently ▁adjust able ▁for wards ▁and ▁back , ▁by ▁either ▁wed ged ▁g ib s ▁or ▁a ▁sc rew ed ▁adjust