<prompt> Hedstrom file having a double helix cross-section and a variation of the Unifile is:Hyflex fileS-fileUnifilesAll of the above  <response>: Modification of Hedstrom file-Hyflex file. It has a cross-section which presents an s shaped instead of the traditional single-helix teardrop cross-section of the Hedstrom file.Unifiles. They are machined from round stainless steel wire by cutting two superficial grooves to produce flutes in a double-helix design. They resemble the Hedstrom file in appearance, are less efficient. They are longer marketedS-files. It has a double-helix cross-section and is a variation of the unifile.Textbook of Endodontics Nisha GARG 3rd ED 