ats ▁made ▁of ▁the ▁same ▁red wood ▁used ▁previously ▁to ▁produce ▁w agon ▁whe els . ▁Hol t ▁sold ▁the ▁first ▁model ▁of ▁steam - power ed ▁tra ctor ▁craw lers ▁for ▁US $ 5 , 5 0 0 . ▁By ▁ 1 9 1 5 , ▁the ▁Hol t ▁company ▁employed ▁ 1 , 0 0 0 ▁workers ▁in ▁its ▁Stock ton ▁plant . ▁Near ly ▁ 2 , 0 0 0 ▁C ater p ill ar ▁craw lers ▁had ▁been ▁sold ▁in ▁more ▁than ▁ 2 0 ▁countries . ▁ ▁Gas oline ▁engines ▁▁ ▁Pl iny ▁E . ▁Hol t , ▁the ▁son ▁of ▁Benjamin ' s ▁half - bro ther , ▁William ▁Harrison ▁Hol t , ▁had ▁been ▁working ▁with ▁Stock ton ▁W heel ▁Company ▁for ▁the ▁past ▁nine ▁years . ▁In ▁ 1 9 0 6 , ▁he ▁was ▁named ▁president ▁of ▁the ▁newly ▁formed ▁Aur ora ▁Engine ▁Company , ▁named ▁after ▁Aur ora ▁Street ▁in ▁Stock ton ▁where ▁it ▁was ▁located . ▁The ▁new ▁company ▁manufact ured ▁gas oline ▁engines ▁to ▁replace ▁the ▁large , ▁heavy ▁steam ▁bo ilers ▁used ▁to ▁power ▁the ▁earlier ▁Hol t ▁tra ctors . ▁A ▁gas oline ▁engine ▁consider ably ▁reduced ▁the ▁overall ▁size ▁and ▁weight ▁of ▁a ▁tra ctor , ▁produced ▁more ▁power ▁per ▁p ound ▁of ▁weight , ▁and ▁reduced ▁the ▁tra ctor ' s ▁cost , ▁making ▁it ▁more ▁cost - effect ive ▁and ▁afford able . ▁Hol t ' s ▁most ▁popular ▁gas oline ▁engine ▁tra ctor ▁was ▁a