Genuine OEM replacement part, this item is sold individually.
This part is used in various places in the compressors listed below.
By its part name, it is used to clamp hoses onto certain parts on the compressors.

This kit includes parts commonly responsible for low compression, including the piston and compression ring. The kit also contains the cylinder tube and head valve o-rings. These parts are genuine OEM Porter-Cable replacement components, not generic or aftermarket. Please note that this kit does not include the valve plate, head gaskets, or any other compressor parts.

This is a genuine Porter Cable replacement part, it is sold individually.
The purpose of the N044359 Tube Seal is to prevent an air leak.
It is placed on the outlet tube coming from the head of the compressor.

Genuine OEM replacement part, this item is sold individually.
The Z-D24819Head Gasket is used on all of the compressor listed below.
It is installed between the Cylinder Head and the Valve Plate.
Its purpose is to make an air tight seal so that no air leakage occurs.
Over time this gasket will deteriorate and will need to be replaced.

Genuine Porter Cable replacement part, this item is sold individually.
Head Gasket Sold Separately.
This part is used in the all of the compressors models listed below.
When air is pumped by the piston it passes through the Valve Plate into the compressor tank.
There are reeds on the valve plate that will eventually wear out, and the Valve plate will need to be replace.
It is advisable at this time to replace the Graphite Gasket Kit, part number D30139.

When you use a compressor the air that is compressed inside the tank will condensate and leave water inside the tank.
If it is left in the tank too long it can start to rust out the inside of the tank.

The Drain Valve should be opened up and let the water drain out.
The water will build up if you have a tendency to leave air in your tank for a long period of time.
You should drain your tank after each time it is used to prevent this from happening.