Ferula (Fer-ROOL-lah) is a spell used by Remus Lupin in 1993, who cast this spell on Ron Weasley to conjure a wooden rod and bandages to use in a splint to help support his broken leg as Hermione Granger, Harry Potter, Peter Pettigrew, Sirius Black and an unconscious Severus Snape left the Shreiking Shack. The spell is described as "bandages spinning up Ron's leg, snapping it tightly to a splint".
"Ferrule" Eng. Wooden handle for strength or protection.