Terminology you'll need to know
Static pressure resistance. Before a system can carry away debris, air already filling the duct needs to be moved out of the way. That produces static pressure resistance measured in inches. Unnecessarily narrow ducts, sharp duct bends, and corrugated hose increase static pressure resistance by restricting airflow or adding friction between ductwork and the air.
Cubic feet per minute (cfm). Be careful how a manufacturer measures air-volume movement. Measurements taken on a "free air" basis—without any attachments that add static pressure or hinder airflow—help you compare one collector with another. But they're not a real-world measure of how a unit will actually perform when hooked up to a system that creates static pressure resistance. Measurements figuring in static pressure resistance better mimic collector performance when hooked up to ductwork and tools.
Drop. A duct descending from an overhead main duct or branch to connect to a tool; drops typically include a 45° wye for the main duct, a 45° elbow, vertical pipe, blast gate, and corrugated hose to attach to the tool. Some use a wye splitter to serve two tools.
FPM/air velocity. This is the speed of air, in feet per minute, moving through the ducts while the system is on. Aim for air velocities of 4,000 fpm in the drops, and 3,500 fpm in the main ducts.
Micron. In this unit of measure for dust particles, 397 microns equals 1⁄64 ".