Concept:
Separators are used in agricultural processing to remove unwanted or dissimilar materials from grains and seeds.
Step 1: Oats may contain impurities or dissimilar grains such as wheat, rye, mustard, and barley.
Step 2: These grains may differ from oats in shape, length, and size.
Step 3: A disk separator is specially designed to separate grains on the basis of length and shape differences.
Step 4: The pockets or cells on the rotating disks pick up particles according to their size and shape.
Step 5: Therefore, for removing dissimilar materials like wheat, rye, mustard, and barley from oats, disk separator is used.
\[
\boxed{\text{Disk separator}}
\]