Reamers: Types, Uses, and How to Choose the Right One
Drilling a hole and finishing a hole are two different operations. A drill bit gets you close — within a few thousandths, usually with a wandering centerline and a rough wall. When the print calls for a tight tolerance, a slip fit, or a bolt hole that actually lines up across three plies of structural steel, the tool that gets you there is a reamer. This guide covers what reamers are, where they earn their keep in fabrication and field work, the difference between machine, bridge, and car reamers, and how to select the right one for the material and tolerance you're working to.
What Is a Reamer?
A reamer is a rotary cutting tool that finishes an existing hole to a precise diameter and a smooth surface. Unlike a drill bit, a reamer removes only a few thousandths of an inch of stock, following the hole already there rather than creating one.
Because a reamer follows rather than cuts its own path, it has multiple flutes — typically four to twelve — that distribute the cutting load and keep the tool centered. That geometry is what produces roundness and a consistent bore. It is also why a reamer will happily follow a crooked hole and produce a perfectly finished crooked hole: reaming corrects size and surface finish, not location.
Reamers are specified by diameter, flute style, shank type, and material. Straight-flute reamers are the general-purpose default. Spiral-flute reamers pull chips up and out, which makes them the choice for blind holes and interrupted cuts such as holes crossing a keyway. Material runs from high-speed steel for general shop work to cobalt and solid carbide for stainless, hardened steels, and production volume. The dimensional standards for these tools are defined in ASME B94.2, the American standard covering reamers.
Field reamers used in structural work are a different animal. A bridge reamer has a long, gradual taper and a hex or square shank, and it is designed to be driven hard to pull misaligned holes into alignment as it cuts. A car reamer is shorter with a steeper taper for lighter alignment work. Both trade fine tolerance for the ability to muscle steel into position.
What Are Reamers Used For?
Reaming shows up wherever hole quality determines whether parts fit or fail. Typical applications include:
- Structural steel erection — aligning bolt holes across beam and column connections when fabricated holes don't line up on site.
- Precision machining — finishing holes to H7 or tighter tolerance for dowel pins, bushings, and bearing seats.
- Hydraulic and pneumatic components — producing the bore finish that seals and valve bodies require.
- Pipe fabrication — removing the internal burr left after cutting so flow isn't restricted and the joint seats properly.
- Machinery repair — restoring worn bores to a nominal oversize dimension for a repair bushing.
- Tooling and fixture work — creating repeatable, accurately located dowel holes for locating pins.
- Bridge and heavy plate work — enlarging and truing holes in thick multi-ply connections.
The structural application deserves particular attention because it is regulated. During steel erection, connections have to be stabilized before the load comes off the hoisting line, and reaming misaligned holes is a routine part of getting bolts through. OSHA's guidance on structural stability during steel erection covers the sequencing requirements that govern this work. For holes that need to be created rather than finished, annular cutters are the more efficient starting point in heavy plate.
How to Choose a Reamer
Five decisions get you to the right tool. Work through them in order.
1. Define the finished hole
Start with the target diameter and tolerance class. Chucking reamers hold roughly ±0.0005 in. in good conditions. If you only need a clean, deburred hole rather than a toleranced one, a deburring tool is faster and cheaper than a reamer.
2. Size the pilot hole correctly
This is where most reaming goes wrong. Leave 0.005 to 0.015 in. of total stock for reamers under 1/2 in., and 0.015 to 0.031 in. for larger diameters. Too little stock and the reamer burnishes instead of cutting, glazing the surface and dulling the tool. Too much and it chatters, producing an oversized, out-of-round hole.
3. Match flute style to the hole
Straight flutes for through holes in steel and cast iron. Spiral flutes for blind holes, interrupted cuts, and softer materials where chip evacuation matters. Left-hand spiral pushes chips ahead of the tool; right-hand spiral pulls them back out.
4. Match material to the workpiece
High-speed steel handles mild steel, aluminum, and brass at moderate volume. Cobalt HSS steps up for stainless and higher-temperature alloys. Solid carbide holds size longest in abrasive material and production runs, at several times the cost and with far less tolerance for deflection or interrupted cuts.
5. Set speed, feed, and coolant
Run a reamer at roughly half to two-thirds the surface speed of the equivalent drill, with a feed rate two to three times higher. Slow and steady is wrong; slow speed with generous feed is right. Always retract with the spindle still turning forward — backing a reamer out in reverse will chip the cutting edges. Use flood cutting lubricant to clear chips and control heat, and manage mist exposure per NIOSH guidance on metalworking fluid hazards.
Reamer vs Drill Bit
These tools are sequential, not interchangeable. The drill makes the hole; the reamer makes it right.
| Drill Bit | Reamer | |
|---|---|---|
| Primary job | Creates a hole in solid material | Finishes an existing hole to size |
| Cutting edges | 2 flutes | 4 to 12 flutes |
| Stock removed | Full hole diameter | 0.005 to 0.031 in. total |
| Typical tolerance | ±0.005 in. or looser | ±0.0005 in. |
| Surface finish | Rough, often with tool marks | Smooth, suitable for slip and press fits |
| Corrects hole location | Sets the location initially | No — follows the existing hole |
Compare options across our reamer selection, and see the full range of twist drill bits for the operation that comes first.
Reamer FAQs
A drill bit creates a hole in solid material, while a reamer finishes a hole that already exists. Drill bits have two cutting edges and hold roughly ±0.005 in. Reamers have four to twelve flutes, remove only a few thousandths of stock, and hold about ±0.0005 in. with a far smoother bore. The two tools are used in sequence, not as substitutes.
Leave 0.005 to 0.015 in. of total stock for reamers under 1/2 in. diameter, and 0.015 to 0.031 in. for larger sizes. Too little stock causes the reamer to burnish rather than cut, which glazes the bore and dulls the edges. Too much stock causes chatter and produces an oversized, out-of-round hole.
Hand drills work for field reamers but not for precision machine reamers. Bridge and car reamers are built for handheld pneumatic or electric drills and tolerate the deflection involved. Machine reamers need the rigidity and alignment of a drill press, mag drill, or mill — a handheld tool will produce a bellmouthed, oversized hole and destroy the tolerance you were reaming for.
A bridge reamer aligns and enlarges bolt holes in structural steel connections during erection. Its long, gradual taper lets ironworkers drive it through misaligned plies and pull the holes into register so bolts will pass. Bridge reamers prioritize alignment force over dimensional precision, which is the opposite of what a machine reamer is built to do.
Yes, for nearly every material except cast iron, which is typically reamed dry. Cutting fluid flushes chips out of the flutes, controls heat that would otherwise expand the workpiece and throw off size, and extends tool life considerably. Sulfurized oils suit steel, while aluminum reams better with a lighter general-purpose or aluminum-specific cutting fluid.
It depends on the trade. Machinists reach for high-speed steel or carbide chucking reamers in fractional and letter sizes for toleranced work. Ironworkers carry bridge and car reamers for field alignment. Pipefitters use tapered pipe reamers to remove internal burrs after cutting. Most shops stock a fractional HSS set and add carbide only for production or abrasive materials.
Ready to Get Started with Reamers?
Midland Tool & Supply has stocked holemaking tooling for the industrial trades since 1962. Shop machine and chucking reamers, field-duty bridge reamers and car reamers for structural alignment, and the rest of our drilling, cutting and holemaking lineup. If you're outfitting an erection crew, pair your reamers with the right spud wrenches for connection work. Ask about our StockUp program to keep consumable tooling on the shelf before a job stalls waiting on a reamer — and if you need help matching a reamer to a tolerance, our team can walk you through it.
