The JBL MTC-419MR MR PLASTER-RING BRACKET (or "Mud Ring") contains a circular offset, forming an edge guide for sheetrock plastering. The bracket has wings that attach to the building structure. Sheetrock is typically either precut or cut with a rotary cutting tool using the outside of the plaster ring circle as a guide. The sheetrock hole is then plastered (or "mudded") up to the ring to create a seamless cutout.