1/4" Quick Change 6" Extenstion, Patented Jaw Design Holds Bits Securely On 6 Flats As Well As Ball Detent Bits, Lock-N-Load System For One Handed Quick Release, 1/4" Range Holds Insert Bits, Carbon Steel Construction Sleeve & Body For Durability & Life, Fits All Irwin Speedbor Blue Grooves, Speedbor Max Sizes: 7/16" To 1-1/4", All Fastener Drives, Unibit Sizes: #1, #2, #10 & #12, 1/4" Hole Saw Arbor Sizes 9/16" To 1-3/16", Countersinks Size #4 To #12.