Proper frame preparation is very important the htr 1b combines reaming and or facing of the head tube to create a perfect fit for most sizes of headset cups the htr 1b comes complete with a 338 mm reamer and four different size pilots 40298 mm 300 mm 338 mm and 368 mm41 the reamer is used to clean out or increase the diameter of the head tube most often facing of the head tube for good cup fit is the objective and no reaming is required in which case the pilots can be us