<P> The spiral may be clockwise or counter-clockwise depending on usage . For example, a tapered hand reamer with a clockwise spiral will tend to self feed as it is used, possibly leading to a wedging action and consequent breakage . A counter-clockwise spiral is therefore preferred even though the reamer is still turned in the clockwise direction . </P> <P> For production machine tools, the shank type is usually one of the following: a standard taper (such as Morse or Brown & Sharpe), a straight round shank to be held by a collet, or a straight round shank with a flat for a set screw, to be held by a solid toolholder . For hand tools, the shank end is usually a square drive, intended for use with the same type of wrench used to turn a tap for the cutting of screw threads . </P> <P> The geometry of a hole drilled in metal by a twist drill may not be accurate enough (close enough to a true cylinder of a certain precise diameter) and may not have the required smooth surface finish for certain engineering applications . Although modern twist drills can perform excellently in many cases--usually producing sufficiently accurate holes for most applications--sometimes the stringency of the requirements for the hole's geometry and finish necessitate two operations: a drilling to slightly undersize, followed by reaming with a reamer . The planned difference between the drill diameter and the reamer diameter is called an allowance . (It allows for the removal of a certain small amount of material .) The allowance should be <0.2 mm (. 008 in) for soft materials and <0.13 mm (. 005 in) for hard materials . Larger allowances can damage the reamer . The drilled hole should not be enlarged by more than 5% of the drilled diameter . Drilling followed by reaming generally produces hole geometry and finish that is as close to theoretical perfection as possible . (The other methods of hole creation that approach nearest to perfection under certain conditions are boring (especially single - point boring) and internal cylindrical grinding .) </P> <P> An adjustable hand reamer can cover a small range of sizes . They are generally referenced by a letter which equates to a size range . The disposable blades slide along a tapered groove . The act of tightening and loosening the restraining nuts at each end varies the size that may be cut . The absence of any spiral in the flutes restricts them to light usage (minimal material removal per setting) as they have a tendency to chatter . They are also restricted to usage in unbroken holes . If a hole has an axial split along it, such as a split bush or a clamping hole, each straight tooth will in turn drop into the gap causing the other teeth to retract from their cutting position . This also gives rise to chatter marks and defeats the purpose of using the reamer to size a hole . </P>

How does a hand reamer differ from machine reamer