To ream multiple hole sizes with the same tool, tighten or loosen the two nuts on these reamers to move the adjustable blades within the diameter range. They’re used for reaming bushings to a precise fit when the size needs to be determined during assembly. Blades can be reground and replaced. To measure size, adjust blades to a known size (such as a bushing or ring), or measure across two opposite blades with a micrometer.