Master Mechanic, 12", Hole Saw Extension, 3/8" Hex Shank Extension Fits Master Mechanic White 1 Piece Bi Metal Hole Saws & Mandrels, Also Designed To Fit Any 3/8" Round Or Hex Shank Tool, The 12" Length Is For Drilling Deep Holes Or For Hard To Reach Areas, Flats On The Shank Provide Positive Driving Action.