Metal Fittings

Metal fittings are the couplings, connectors, elbows, bushings, locknuts, and conduit bodies that join conduit, change its direction, and tie it into boxes and enclosures. The original job was simple — protect the wires inside from mechanical damage. But the metallic raceways of today serve a second purpose. They carry fault currents, which are potentially lethal. That means special attention to component selection, preparation, and assembly.

Here’s the one thing that matters most: match the fitting to three things — the conduit type, the connection method, and the location rating. Get that combination right and the system stays safe, grounded, and code-compliant. Get it wrong and you’ve built a grounding failure into the wall.

This guide is for contractors, electricians, and serious DIY builders wiring a building who need to pick fittings that hold up.

Matching Fittings to Your Conduit Type

Every conduit type dictates which fittings work with it. There’s no universal connector.

EMT (electrical metallic tubing) is the thin-walled stuff — light, cheap, easy to bend with hand tools. The catch is workers need fittings and couplings, like compression fittings and set screws, to connect pieces together. EMT suits indoor commercial and residential runs where the damage risk stays low.

IMC (intermediate metal conduit) runs a thinner wall than rigid but is easier to work with and more cost-effective. It offers strong protection for wire and cable and is often used when GRC might be overkill. IMC uses threaded steel or aluminum fittings for stronger commercial and industrial installs.

RMC / GRC (rigid metal conduit / galvanized rigid conduit) is the heavy hitter. Galvanized rigid conduit is a strong, durable, thick-walled steel tubing made using a hot-dip galvanization process to help avoid corrosion. The trade-off: GRC is heavy and sometimes difficult to work with, and if workers need to change direction for a bend, they need threaded fittings and bending tools. It belongs in industrial and harsh outdoor environments.

One detail that saves you money and shelf space: both IMC and RMC have the same outside diameter, so they use many of the same fittings. This interchangeability makes retrofits easier and reduces the parts you need to keep on hand.

Conduit Type	Wall	Connection Method	Best Use
EMT	Thin	Set-screw or compression	Indoor commercial/residential, low damage risk
IMC	Medium	Threaded steel or aluminum	Commercial/industrial
RMC/GRC	Thick	Rugged threaded	Outdoor, underground, harsh/corrosive

Connection Methods and Location Ratings

For unthreaded conduit, you’ve got two families. The unthreaded fittings fall into two general categories: gland (compression) type and set screw type. Gland type is the only type of unthreaded fittings listed for use in wet locations. Set-screw is dry-location work. Don’t mix the two — use only one type of fitting for a job. Otherwise, electricians will have to play mix-and-match games that slow down the work and increase the cost of labor.

Torque matters. When set-screw fittings are tested to UL 514B, the torque value used for a No. 8 screw is 20 lbf-in, a No. 6 screw is 12 lbf-in, and all other size screws is 35 lbf-in — unless the manufacturer specifies otherwise.

Compression fittings tighten harder, and the spec climbs with trade size:

Trade Size	Compression Torque
1/2”	300 lbf-in
3/4”	500 lbf-in
1”	700 lbf-in
1-1/4”	1000 lbf-in
1-1/2”	1200 lbf-in
2”–4”	1600 lbf-in

On grounding — this is why the listing matters. One of the major benefits of steel raceways is that they can be used as an equipment grounding conductor per NEC Sections 342.60, 344.60, 358.60, and 250.118. To earn that trust, all fittings and connectors associated with them must pass a resistance and continuity test to confirm that they can provide an effective ground-fault current path to receive a product listing under safety standard UL 514B.

Location rating is where Montana installs get tripped up. Outdoor, underground, and below-grade runs are wet locations. When installing steel raceways below grade, in concrete slabs, in direct contact with the earth, and in locations subject to saturation with water, it is considered a “Wet Location” by the National Electrical Code. Look for the package or label to state “Wet Locations” and list to UL 514B and/or CSA C22.2 no. 18.3-12. Sometimes the marking reads “Raintight” instead — but raintight does not mean waterproof. For prolonged submersion in water, use NEMA 6 or 6P fittings.

Pouring conduit into a slab? Compression-type fittings are concrete-tight if they are listed to the UL or CSA standards. Set-screw fittings are a different story — they may be required to be taped to be concrete-tight, in which case the markings will state “Concrete-tight when taped” or similar wording. And don’t confuse the two ratings: a concrete-tight fitting isn’t automatically watertight or raintight — those require specific listings. However, fittings listed as raintight automatically qualify as concrete-tight.

Choosing Material for the Environment

The Code doesn’t force a material on you. Fittings come in several materials, including cast aluminum, cast malleable iron, cast zinc, and fabricated steel. Because all listed fittings meet minimum performance criteria, the Code doesn’t specify what type of material you should use. You base the decision on design considerations or personal preference.

Burial is the exception where material choice gets real. In certain soils you should use cast malleable iron; in others, cast aluminum works best. If you’re going to bury conduit, find out what is customary for the locale — your local distributor will know which material most installers use and may stock only fittings of that material.

For corrosion resistance, stainless steel splits into two grades. 304 stainless is the choice for wet and outdoor environments, while 316 stainless is the most corrosion-resistant — it won’t degrade when exposed to salt water and harsh chemicals.

Aluminum earns a look on big jobs and in salty air. Lightweight aluminum makes sense for aerial applications and is easier to move and handle, though it’s weaker than steel and may undergo galvanic corrosion if improperly installed. Worth knowing for coastal-style exposure: aluminum holds up well where salty air is a problem, and saltwater is corrosive, but aluminum forms aluminum oxide as it corrodes for added protection.

Liquid-tight fittings run the full material range — malleable iron, copper-free aluminum, zinc die cast, tubular steel, 304 stainless steel, and non-metallic nylon — in trade sizes from 3/8” through 6” in straight, 45°, and 90° configurations. Stainless conduit fittings commonly cover trade sizes 1/2” through 4” in straight, 45° elbow, and 90° elbow shapes for IMC and RMC.

The Fitting Families, and What Each Does

• Couplings — join conduit “sticks” together for a long straight run and join site-fabricated bends to conduit.
• Combination (transition) couplings — make the transition from a GRC/IMC raceway to another type, such as EMT or flexible metallic conduit. Reducers are included in this family.
• Connectors — attach conduit to boxes, enclosures, or panels for secure terminations.
• Elbows — change the direction of the raceway by 90°. Used properly, they save significant labor and improve the appearance of the install, with 45° versions for smoother direction changes.
• Bushings — provide a smooth, rounded conduit entry to protect the conductors during wire pulls. Extremely important when transitioning from the conduit system into an enclosure.
• Conduit bodies — tiny pullboxes. When you need a splice somewhere between the two ends of a run, install a conduit body. They’re also useful for changing direction and allowing access to conductors in a completed system.
• Hubs — give a threaded entry when a box doesn’t have one. Use a hub when you run conduit to a box without an integral hub — never run conduit straight through a hole in a box.
• Locknuts — any time a fitting enters a box, secure it with a locknut. If the nut has teeth on only one side, install it with the teeth biting into the box.
• Reducers — connect conduits of different sizes.
• Drains — if conduit runs from a warm area to a cool one, you can expect condensation. Install a drain at the lowest point of the run and anywhere water might accumulate.
• Expansion fittings — if you run conduit between two areas where the temperature varies significantly, use expansion fittings. They reduce stress on the raceway and its supports.

Western Building Center’s box-connector lineup includes zinc clamp connectors in 3/4”, 1”, and 1-1/2”, a 1/2” watertite cable connector, steel knockout seals, and Halex die-cast zinc clamp connectors and steel knockouts in 3/8” and 1/2”.

A Few Notes for Montana Installs

Two of these fittings earn their keep in this climate. Conduit running between a heated space and a cold one will sweat — that’s the drain fitting’s whole job, set at the low point of the run. And across the wide seasonal swings most of the state sees, expansion fittings keep temperature movement from stressing the raceway and its supports.

Support is non-negotiable. NEC Section .30 of Articles 342, 344, and 358 requires conduit and tubing be supported every 10 feet and securely fastened within 3 feet from every box or termination. Improper securement puts extra strain on the fitting, possibly leading to a premature failure.

Frequently Asked Questions

Can I mix set-screw and compression fittings on one job? Don’t. Stick to one fitting type per job. Mixing them forces crews into mix-and-match work that slows the install and drives up labor cost. Pick the method that fits your location rating and stay consistent.

Does “raintight” mean a fitting can be submerged? No. Raintight does not mean waterproof. For prolonged submersion in water, you need NEMA 6 or 6P fittings. Raintight handles weather exposure, not standing or submerged water.

What’s the difference between 304 and 316 stainless fittings? 304 stainless is the general choice for wet and outdoor environments. 316 is the upgrade for the harshest exposure — it won’t degrade against salt water and harsh chemicals. If corrosion is severe, step up to 316.

Will the fittings ground my system, or do I need a separate ground wire? Steel raceway can serve as an equipment grounding conductor under the NEC, but only if the fittings are listed to UL 514B. That listing means the fitting passed resistance and continuity testing to confirm an effective ground-fault current path. Look for the listing mark.

Can I use the same fittings for IMC and RMC? Often, yes. IMC and RMC share the same outside diameter, so many fittings work on both. That interchangeability makes retrofits easier and cuts down on the parts you have to stock.

What torque do set-screw fittings need? Per UL 514B testing: 20 lbf-in for a No. 8 screw, 12 lbf-in for a No. 6, and 35 lbf-in for all other sizes — unless the manufacturer specifies a different value, in which case follow the manufacturer.