Our lower unit rebuild kit contains several parts which are used in building a lower unit. These parts include gears, bearings, seals and nuts and screws. All these things are required for proper functioning of the lower unit. If these parts are worn-out due to excess usage, then the rebuild kit is what needed to replace those worn-out parts or completely rebuild lower unit. So you can use Yamaha rebuild kit specified for your outboard engine which has all the required parts to get the job done.