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very length of EMT you buy is made to a standard — ANSI C80.3. It fixes the outside diameter, the wall thickness and how far each can vary. Get familiar with those three numbers and a spec table stops being a wall of digits and starts telling you exactly what will happen on site.

The standard exists so that a connector from one maker seats on tubing from another, and so that a bender set up for a given size produces a repeatable result. When the dimensions drift, fittings bind, offsets spring back unpredictably and inspectors start asking questions.

The Three Numbers That Matter

For any trade size, a C80.3 table gives you the nominal outside diameter, the nominal wall thickness, and the tolerance band around the O.D. Here’s a slice of the EMT range so you can see how they scale:

Notice the wall doesn’t grow in lockstep with diameter — it steps up in bands. That’s why a 2″ and a 1-1/4″ can share the same wall thickness while their diameters differ significantly.

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Tolerance Isn’T Slack In The Product — It’S The Promise That

Every Piece Falls Inside A Known Window.

Reading The Tolerance Band

C80.3 tightens or loosens the allowed O.D. variation by size. Smaller conduit is held to a few thousandths of an inch; the largest sizes get a slightly wider band because they’re harder to form to the same absolute precision. A typical set of bands looks like this:

• Trade sizes 1/2″–2″: ±.005 in (.13 mm)
• Trade size 2-1/2″: ±.010 in (.25 mm)
• Trade size 3″: ±.015 in (.38 mm)
• Trade sizes 3-1/2″–4″: ±.020 in (.51 mm)

What To Check Before You Order

Confirm the standard on the datasheet, verify the length and its tolerance, and make sure the finish suits the environment. If any of those are missing from a supplier’s table, that’s your signal to ask. You can always pull the full figures from our specification tables or the EMT product page.