The UNIQUE Core Bore Seal Firestop System is a revolutionary way to firestop, water and smoke-seal abandoned empty core holes from 1.5 to 5.5 inches in fire-rated concrete slabs. No need to access the floor below during installation! Choosing the size is simple. Choose the diameter closet to the diameter of the hole with out going bigger than your hole. Example: If your hole is 3 5/8 you would choose the CBS-35 3 1/2. Core Bore Seals rang from 1.5 in. to 5.5 in. in half inch increments. Our CBS Firestop System was UL tested using Silicone Firestop Sealant STI brand sealant SIL300 sold seperatly.