Proper frame preparation is very important The HTR-1B combines reaming & / or facing of the head tube to create a perfect fit for most sizes of headset cups The HTR-1B comes complete with a 33.8 mm reamer & four different size pilots (29.8 mm 30.0 mm 33.8 mm & 36.8 mm) 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 & no reaming is required in which case the pilots can be used in place of the reamers The unique quick-release quick-adjust feature means that you can slide the bottom portion on & off easily without the long threading process This threading function of the tool can still be fine tuned whilst in use The tapered centring cone unit rides on a bearing for extra smooth operation All cutting surfaces are finest top quality & extra sharp