A common item found in an insulator's tool bag is a radius divider. These sheet metal tools are used to make circles and semi-circles (fish mouths) on both metal jacketing as well as pipe insulation. The divider consists of two legs with points that can be adjusted to different radiuses. The one point stays put while the other leg is dragged around the center point marking the outer circle which can later be cut out.
We offer two common dividers:
Malco #24 Radius Divider - makes circles with a maximum diameter of 42".
Flat Legged Wing Divider - Comes in a variety of sizes.