▁agricult ural ▁tra ctors ▁and ▁mount ▁to ▁the ▁tra ctor ' s ▁three ▁point ▁h itch . ▁The ▁broadcast ▁seed ers ▁that ▁are ▁mounted ▁to ▁a ▁three - point ▁h itch ▁are ▁power ed ▁by ▁a ▁power ▁take - off ▁( P . T . O .) ▁sh aft ▁from ▁the ▁tra ctor . ▁At ▁the ▁largest ▁size ▁are ▁pull ▁behind ▁or ▁ch ass is ▁mounted ▁units ▁for ▁agricult ural ▁use ▁that ▁can ▁spread ▁width s ▁of ▁up ▁to ▁ 9 0 ▁feet . ▁ ▁How ▁they ▁work ▁▁ ▁The ▁basic ▁operating ▁concept ▁of ▁broadcast ▁spread s ▁is ▁simple . ▁A ▁large ▁material ▁ho pper ▁is ▁position ed ▁over ▁a ▁horizontal ▁spin ning ▁disk , ▁the ▁disk ▁has ▁a ▁series ▁of ▁ 3 ▁or ▁ 4 ▁fins ▁attached ▁to ▁it ▁which ▁throw ▁the ▁dropped ▁materials ▁from ▁the ▁ho pper ▁out ▁and ▁away ▁from ▁the ▁se eder / sp reader . ▁Altern ately ▁a ▁p end ul um ▁spread ing ▁mechanism ▁may ▁be ▁employed , ▁this ▁method ▁is ▁more ▁common ▁in ▁mid - s ized ▁commercial ▁spread ers ▁for ▁improved ▁consist ency ▁in ▁spread ing . ▁The ▁photos ▁clearly ▁show ▁the ▁material ▁ho pper . ▁Ho ppers ▁are ▁commonly ▁made ▁of ▁pl astic , ▁painted ▁steel , ▁or ▁st ain less ▁steel . ▁St ain less ▁steel ▁is ▁usually ▁used ▁in ▁large ▁commercial ▁units ▁for ▁strength ▁and ▁because ▁gran ular ▁fert il izer ▁is ▁often ▁quite ▁cor ros ive . ▁ ▁Some ▁seed ers / sp read ers ▁have ▁direction al ▁fins ▁to ▁control