What are the tractor requirements for these Chippers and Chipper/Shredders?

The Crary® Bear Cat® 4.5″ Chipper requires a tractor with PTO horsepower ranging from 20 hp to 35 hp. The Crary Bear Cat 5″ Chippers and Chipper/Shredders require a tractor with PTO hp ranging from 25 hp to 45 hp. The Crary Bear Cat 9″ Chippers require a tractor with PTO hp ranging from 35 hp to 60 hp. The Crary Bear Cat 9” high horsepower chippers (HP models) require a tractor with PTO hp ranging from 50 hp to 100 hp.