The purpose of the Spindle is to control the safe rotation of the mower blade during operation. The spindle is often made of aluminum on residential mowers and steel on commercial mower decks. Much like a rotating pin in other applications, the spindle is designed to break if the blade hits a hard object to protect the deck shell from damage. The self-tapping screws required for installation (usually sold separately) will create the threads as they are drilled into the bare holes in the spindle. OakTen offers one year warranty for all the deck spindles sold, verify the OEM part number by referring engine model number and the parts manual.