I recently, in a weak moment, purchased a three piece set (1/4, 3/8 and 1/2 diameter) of High Speed Steel spiral mortising bits, Harbor Freight #66733. Have used the 1/2 and 1/4 bits and was pleasantry surprised. They worked better and cut cleaner that I expected. At 12 or 13 dollars without the 20% discount they may be hard to beat. I usually shy away from buying cutting tools at HF, and its unknown if these bits will hold-up, but so far so good.