CAT tooling comes in a range of sizes designated as CAT 30, CAT 40, CAT 50, etc. The number refers to the Association for Manufacturing Technology (formerly the National Machine Tool Builders Association (NMTB)) Taper size of the tool. CAT tooling is sometimes called V-Flange Tooling. CAT Tool Holders will accept both Imperial and metric sized tools. CAT tapered tool holders are similar to BT tapered tool holders. The difference between CAT and BT is the flange style, thickness, and the thread for the pull stud is a different size. CAT Tooling uses Imperial (English) thread pull studs (retention knobs).