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Without a good clipper, doing undercut hair for men can be difficult.  Ideally, your clipper will be a single-length clipper. But if you want to do fading and tapering, you will need a clipper that allows length adjustments.  The ideal clipper to do undercut hair for men is one of high quality and high durability.  An Andis cordless clipper, for instance, is a popular option.  As for corded clippers, an Andis or Oster model is preferable. With a single-length clipper, choose one that is numbered one, two, or three.  You could also use a number zero, but this tends to be too short.  A clipper set at four or above is usually too long, though some men might want to “test drive” an undercut by getting the short part of their hair clipped with a number four clipper. The temples are the corners of the hairline where the hairline curves and thins, and provide an important guide when trying to do undercut hair for men.  The temples sit in different locations on each person’s face.  To identify a person’s temples, first locate their hairline, the place where their hair meets their forehead.  You might also be able to locate the temple based on the position of the ears.  The tops of the ears, traced forward to the edges of the face, typically intersect the temples. Trace the hairline to its outer edges on the left and right side. When you notice the hairline angle up and out, you’ve located the upper temple. Parting the hair will make it easier for you to see which hair you need to be cutting. Make a clean part and then clip the long hair on the top of their head back so it's not in your way. If their hair is too short to clip back, use water or a styling product to keep their hair parted.
Choose the right clipper for the person's hair. Identify their upper temple area. Part their hair where you want to disconnect it.