Gear kit for the HP LaserJet P3015 M521 or M525 series printers. This kit contains four (#1-4 pictured) drive gears, they sit at the back of the printer behind the fuser. If you have replaced the P3015 fuser and your printer sounds different (you hear rumbling or noisy gear sounds) you should replace these gears. These gears commonly wear out on the P3015 , M521, and M525 series printers. Note: one of the gears, the fuser drive gear, in the M521/M525 looks slightly different than the P3015 replacement gear, however it does work. The fuser drive gear for the M521/M525 is not available so the gear in this gear kit is the best replacement option for the M521 and M525 series printers.