The 1-quart pressure cup is perfect for small painting jobs that require pressure to assist in fluid delivery without the ability to adjust the cup pressure. The cup is aluminum and is fitted with a one-way check valve to prevent fluid from going back up into the gun. It is designed for HVLP use, connects to head of gun, and has a max pressure of 10 psi. (Note- Pressure assist cups require a ported spray gun for operation.). 51-350 has a screw lid with a max pressure of 50 psi.