The Milwaukee 7-1/2 in. extension for large thin wall core bits expands your drilling capacity. Made of high-quality steel, the extension extends your drilling by up to 7-1/2 in.. it attaches easily to SDS plus core bit adapters and features smooth, tough thin core construction for dependability. For deeper drilling, use the extension with a Milwaukee 8 in. or 12 in. SDS plus adapter shank.