Reaming Flutes

Reamer flute choices vary from straight flutes to flutes having a right hand spiral (RHS) or left hand spiral (LHS) orientation. For all practical purposes, they are all right hand cut (RHC) regardless of flute spiral direction.
There are some guidelines however as to when Straight, RHS or LHS flutes are appropriate.

Straight-fluted RHC reamers are for general-purpose use in a wide range of materials. They are best in through holes less than 2 diameters deep.

RHS/RHC reamers are normally chosen for blind holes or deep holes as they carry cut chips back up out of the hole. They are free cutting and normally produce a better finish. Right hand spiral reamers are particularly well adapted to cutting aluminum alloys, copper and other free-cutting non-ferrous material.

LHS/RHC reamers are an advantage in through holes as they push troublesome chips ahead of the tool. They are most often used in steels and irons. They do consume more torque to operate but can reduce chatter in less than ideal setups.