These Agilent Varian HS-20 diffusion pump replacement foreline baffle assemblies are OEM Agilent Varian replacement parts with part number 84889301. The foreline baffle is located in the roughing line exhaust arm of the diffusion pump. They are designed to help prevent diffusion pump oil from being transported to the roughing pump under high throughput conditions. See the HS-20 diffusion pump roughing line arm noted by balloon #5 in the illustration below.