Something to consider before buying is to measure the shanks of your forstner bits. I thought I had a pretty decent set of bits and the shanks aren't all mixed up, but they are between .370" and .377" in diameter. The bit extender I received measures .376 inches. The extension is advertised for a 3/8" shank and it fits a .375" shank. it will take more than a little bit of sandpaper to reduce the diameter. 5 of my 16 bits are too big to fit.