Choosing a Reamer: Seven Classification Axes, 15 Types, Flutes and Angles

Before asking which reamer to buy there are seven things to settle: hand or machine, cylindrical or tapered bore, solid or shell, adjustable diameter or not, tool material, cutting edge or burnishing, straight or helical flute. Those seven axes decide the type, and the type decides flute count and angles. This article lays out the seven axes, 15 common types with their diameter ranges, the flute count tables and the four angles that matter, so you know what you are asking for before you request a quote.

1. First decide: hand or machine

This is the first of the seven axes because it sets the shank, the angles and the accuracy you can reach all at once.

The shank is the quickest identifier: a square drive means hand reamer. Its lead angle is deliberately small so a person can turn it and so the tool finds the bore.

2. The seven classification axes

These are not seven alternatives, they are seven fields that all have to be filled in. Fill them in when you request a quote and nobody has to come back and ask - this is also why one diameter comes back with several prices. For how to write an RFQ for other cutting tools, see How to Write a Cutting Tool RFQ (Request for Quotation): Part Number, Specs, Work Material, Quantity and Lead Time in One Go.

3. Fifteen common types: diameter decides your shortlist

Read this table by finding your diameter band first, then checking for a special need: holding pitch, an end radius, or saving material. Above 80 mm the inserted blade type is essentially the only route left.

4. Flute count: diameter decides, material trims

More flutes is not better. Two rules: larger bore, more flutes; fewer flutes in tough materials, more in brittle ones.

These two tables come from a different source than the type table above, so the same diameter is not guaranteed to agree between them. Buy against the maker's specification and the drawing.

5. Straight or helical: a left hand helix cannot ream a blind hole

🔴 A left hand helix pushes chips forward, so it cannot ream a blind hole.
Right and left hand feed forces act in opposite directions, so a right hand reamer is less securely held than a left hand one, and its parameters must be kept lower. Those two sentences are the pair most often missed when choosing a helical reamer.

Helix angle B follows the material: grey iron and hard steel take 7~8 deg; malleable iron and general steel 12~20 deg; aluminium and light alloys 35 deg.

6. Four angles: ask about the lead angle first

Ask about the lead angle first, because it follows the form of the bore: 12~15 degrees for a through bore, but 45 degrees for a blind one - a large jump. Rake is usually 0 degrees because the reaming allowance is small to begin with (typically 0.06~0.30 mm), so the chip is thin and only touches near the edge; rake has no marked effect on deformation, and 0 degrees is simply easier to make and regrind. Clearance is kept large because reaming takes a thin chip and wears the flank noticeably, and a larger angle makes the diameter change more slowly as it wears.

For regrinding the reamer itself see Regrinding a Reamer: Rake Face, Flank and How Fine the Ground Surface Must Be; for carbide and special structures see Regrinding Carbide and Special Reamers: Tilt Angle, Transition Edge Position and Three Structures.

Once the reamer is chosen, for what tolerance the bore can reach and how the drill-ream-bore route is planned, see How to Improve Hole Accuracy: IT Tolerances and the Drill / Ream / Bore Route; for the holder, see Tool Holders for Reaming: Floating Is a Tapping Answer.

Published: 2026-09-19｜Last updated: 2026-10-28