What Is a Reamer? Car, Bridge and Pipe Reamers Explained

What is a reamer, and how is it different from a drill bit?

A reamer is a cutting tool that takes a small amount of metal out of an existing hole to make it larger, rounder, straighter or better lined up. A drill bit makes a new hole from solid material. A reamer cannot start a hole; it needs one to follow. Reamers have many straight or spiral cutting edges along the side, which is why they leave a smoother, truer hole than a drill.

On a job site, reaming usually means one thing: two plates or a beam and a clip whose bolt holes don't quite line up. A tapered reamer runs through both holes at once and leaves one round hole the bolt slides through.

What are the types of reamers?

Reamers fall into two groups: construction reamers for lining up bolt holes in the field, and machine reamers for precise holes in a machine shop. This table lists the common types of reamers and what each one is for.

We focus on the reamers contractors and fabricators use. For hand, chucking and taper pin reamers, a machine shop supplier is the right call.

Car reamer vs bridge reamer: what is the difference?

A bridge reamer has a longer flute than a car reamer, so it can ream through a thicker stack of steel in one pass. Both have a long tapered point that starts in a misaligned hole, a left-hand spiral that keeps the reamer from screwing itself into the work, and a right-hand cut. Pick a car reamer for most connections and a bridge reamer for thick plate or multi-ply stacks.

The point diameter is the smallest opening the reamer will start in. A 13/16 in. reamer has a 0.468 in. point, so it will enter any gap between two holes that is at least 15/32 in. across, then cut both holes round as it feeds in.

What size reamer do I need for a bolt?

Size the reamer to the bolt hole, not the bolt. A standard hole for a structural bolt is the bolt diameter plus 1/16 in. (AISC 360, Table J3.3), so a 3/4 in. bolt takes a 13/16 in. reamer. This table gives our three most common reamers for each bolt size.

Store prices on Oct 2, 2026. Reamers are sold one at a time.

For 1 in. bolts, the current AISC specification calls for a 1-1/8 in. standard hole, and older drawings often show 1-1/16 in. We stock 1-1/16 in. reamers (CHX-6864, $109.83 each) and car reamers up to 1-1/4 in. Always ream to the hole size on the drawings. Reaming a hole past its standard size makes an oversized hole, which needs the engineer of record's OK on structural work.

Which reamer line should I buy?

All six of our car and bridge reamer lines are ITM, made of M2 high-speed steel, with a tapered point and left-hand spiral. They differ by shank, flute and where they are made. Prices are for the 13/16 in. size.

If the reamer goes in a 1/2 in. drill or a magnetic drill with a chuck, buy a 3-flat shank. If your crew runs hex-drive reamers, buy the hex line. Pay for USA-made when the job specs it or the reamer will see daily use.

"When the holes don't line up, don't reach for the torch. A car reamer cleans up both plates in one pass and leaves a round hole the bolt will actually fit."

David Castro, President, Eldorado Tools

How do you use a car reamer?

Run a car reamer slowly, with steady pressure and cutting oil, and always forward. Reaming takes far less metal than drilling, so the reamer should cut, not rub.

• Clamp or bolt the pieces. Pin the connection with drift pins or a few bolts so the plates can't shift while you ream.

• Run about half drill speed. A reamer runs at about half the RPM of a drill bit the same size. See the table below.

• Use cutting oil. Oil on steel and stainless keeps the edges cool and the hole smooth.

• Feed steadily through. Let the taper pull the holes into line. Don't force it sideways.

• Never run it in reverse. Backing a reamer out in reverse drags chips across the edges and dulls them. Pull it out while it turns forward, or stop it and lift it out.

Starting speeds use half the drilling surface speed from our drill speed chart: 45 surface feet per minute in mild steel and 20 in stainless. Most corded 1/2 in. drills have a low gear in this range.

What is a pipe reamer?

A pipe reamer removes the sharp burr a saw or cutter leaves inside a cut pipe or conduit. The burr chokes flow in a pipe and cuts wire insulation in conduit, and the electrical code requires the cut ends of EMT conduit to be reamed (NEC 358.28). Our pipe reamers have hex shanks (1/4 in. on the small sizes), so they run in a drill or impact driver.

An outer chamfer reamer bevels the outside edge of a pipe, rod or bolt so a fitting slides on and a nut threads onto cut threaded rod. Pick carbide blades for stainless steel and daily use, and HSS for occasional work in mild steel, copper and plastic.

Why won't my reamer cut?

A reamer that won't cut is usually running too fast, has been run in reverse, or is trying to remove too much metal. This table covers the common problems.

Drilling the holes first? See How to Choose Drill Bits for Metal and Types of Drill Bits Explained. Questions about a job? Call our team at (833) 4-ETOOLS or email sales@eldoradotools.com.

First published June 12, 2023. Rewritten Oct 2, 2026 with bolt-size, speed and pipe reamer tables and priced picks.