**Dear Mr. Electrician:** What are one inch electrical conduit dimensions?

**Answer: **One inch electrical conduit dimensions are not the same as the trade size. 1″ is the trade size and twenty seven (27) is the metric designator not the actual dimension in millimeters. NOTE: Text links below go to applicable products on Amazon. As an Amazon Associate I earn from qualifying purchases.

Use an 1 3/8″ (35mm) hole saw for 1″ conduit fittings.

**The dimensions for various types of 1″ electrical conduits are below.** The information was derived from several sources and should not be considered precise. Dimensions may vary slightly between manufacturers.

1″ **Electrical Metallic Tubing** (**EMT** or Thinwall) is a smooth lightweight galvanized metal conduit that has an inside diameter of 1.049″ or 26.64mm. The outside diameter is 1.163″ or 29.54mm. The wall thickness of 1″ EMT is 0.057″ or 1.45mm.

100 feet of 1″ EMT weighs approximately 67 pounds or 30.4 kilograms. It requires a 1 3/8″ hole for the conduit fittings. A tap needs a 1 5/32″ hole. Threads per inch for the fittings is 11.5, NPT.

1″ **Rigid Metal Conduit** (RMC) is a heavy weight conduit with a galvanized finish throughout. It has factory threads with a 3/4″ per foot taper, 11.5 threads per inch NPT. 100′ of 1″ RMC weighs approximately 161 pounds or 73 kilograms.

One inch RMC has an inside diameter of 1.049″ or 26.64mm It has an outside diameter of 1.315″ or 33.4mm. The wall thickness is 0.126″ or 3.20mm. 1″ Rigid requires a 1 3/8″ hole for the conduit and fittings. A tap needs a 1 5/32″ hole.

1″ **Intermediate Metal Conduit** (IMC) is a lighter weight version of RMC. It has a galvanized finish inside and out and can be used in many of the same environments as RMC. It has factory threads with a 3/4″ per foot taper, and 11.5 threads per inch NPT. It also utilizes the same couplings and **fittings** as RMC.

100 feet of 1″ IMC weighs approximately 119 pounds or 54 kilograms. 1″ IMC has an inside diameter of 1.120″ or 28.1mm. It has an outside diameter of 1.29″ or 32.8mm. The wall thickness is 0.093″ or 2.35mm.

**CLICK HERE to See Conduit Bodies Sold on Amazon**

1″ **Flexible Metal Conduit** (FMC or Greenfield) is a galvanized finished **flexible metal electrical conduit** composed of a continuously formed interlocking metal strip.

100 feet of 1″ Reduced Wall Steel Greenfield weighs approximately 57 pounds (25.854744 kilograms). Reduced Wall 1″ Aluminum FMC weighs 20 pounds or 9.07 kilograms.

1″ FMC has a minimum inside diameter of 1.000″ or 25.4mm and a maximum inside diameter of 1.040″ or 26.416mm. It has a minimum outside diameter of 1.300″ or 33.02mm and a maximum outside diameter of 1.380″ or 35.052mm. The minimum bending radius is 6 inches or 152.4mm. 1″ Flex requires a 1 3/8″ hole for the conduit fittings. A tap needs a 1 5/32″ hole. Threads per inch for the fittings is 11.5, NPT.

1″ **Rigid Polyvinyl Chloride Conduit (PVC) schedule 40** is a nonmetallic, non-conductive electrical conduit that is good to use indoors and outdoors, or underground. It has some flexibility with an inside diameter of 1.049″ or 26.64mm. It has an outside diameter of 1.315″ or 33.40mm. The wall thickness is .133″ or 3.38mm.

1″ Schedule 40 weighs 34 pounds per 100 feet (15.42 kilograms). 1″ PVC requires a 1 3/8″ hole for the conduit fittings. A tap needs a 1 5/32″ hole. Threads per inch for the fittings is 11.5 NPT.

1″ **Rigid Polyvinyl Chloride Conduit (PVC) schedule 80** is a nonmetallic, non-conductive electrical conduit that is good to use indoors and outdoors, or underground. It has limited flexibility.

Schedule 80 has an inside diameter of .957″ or 24.31mm. It has an outside diameter of 1.315″ or 33.40mm. The wall thickness is .179″ or 4.55mm. 1″ Schedule 80 weighs 44 pounds per 100 feet or 19.958048 kilograms. 1″ PVC requires a 1 3/8″ hole for the conduit fittings. A tap needs a 1 5/32″ hole. Threads per inch for the fittings is 11.5 NPT.

1″ **Electrical Nonmetallic Tubing** (ENT or **Smurf**) is a nonmetallic, non-conductive flexible conduit with an inside diameter of 1″ or 25.4mm. It weighs 20 pounds per 100 feet or 9.07184 kilograms.

1″ ENT has an outside diameter of 1.315″ or 33.40mm. The minimum bend radius is 6 inches. 1″ fittings requires a 1 3/8″ hole. A tap needs a 1 5/32″ hole. Threads per inch for the fittings is 11.5.

1″ **Liquidtight Flexible Metal Conduit** (LFMC or Sealtight) is a flexible metal conduit with a non-metallic, non-conductive outer jacket that makes it suitable for use in wet locations. 100 feet of 1″ Sealtight weighs 78 pounds or 35.38 kilograms.

One inch Sealtight has an inside minimum diameter of 1.041″ or 26.44mm and a maximum inside diameter of 1.066″ or 27.08mm. It has a minimum outside diameter of 1.290″ or 32.766mm and a maximum outside diameter of 1.315″ or 33.40mm. The minimum bending radius is 6 inches (152.4mm). Fittings requires a 1 3/8″ hole. A tap needs a 1 5/32″ hole. Threads per inch for the fittings is 11.5 NPT.

1″ (27) **Liquidtight Flexible Nonmetallic Conduit** (LFNC or CarFlex) is a nonmetallic conduit that is suitable for wet conditions. 100′ of 1″ Carflex weighs 28 pounds. It has an inside minimum diameter of 1.041″ or 26.44mm and a maximum inside diameter of 1.066″ or 27.07mm.

One inch LFNC has a minimum outside diameter of 1.290″ or 32.76mm and a maximum outside diameter of 1.315″ or 33.40mm. The minimum bending radius is 6 inches or 146mm. It requires a 1 3/8″ hole for the conduit fittings. A tap needs a 1 5/32″ hole. Threads per inch for the fittings is 11.5 NPT.

1″ **Reinforced Thermosetting Resin Conduit** (RTRC or Fiberglass) is a nonmetallic conduit that is suitable for many conditions. It has an inside diameter of 1.175″ or 29.84mm. Outside diameter is 1.315″ or 33.40mm.. The conduit wall thickness is .070″ or 1.778mm.

100 feet of one inch RTRC weighs 19 pounds or 8.618248 kilograms. It requires a 1 3/8″ hole for the conduit fittings. A tap needs a 1 5/32″ hole. Threads per inch for the fittings is 11.5 NPT.

1″ **High Density Polyethylene** (HDPE) is a non-metallic flexible conduit available in long reel lengths to reduce joints and installation time. It has an outside diameter of 1.315″ or 33.40mm.

Type SDR-9 has an inside diameter of 1.003″ or 25.4762mm. 100 feet of 1″ HDPE weighs 24 pounds. The wall thickness is 0.146″ or 3.7084mm.

**All one inch 1″ (27) conduit and fittings** require a inch and three eighth 1 3/8″ (35mm) opening into an electrical box. The hole can be made with a hole saw or a knockout punch.

A tap for one inch 1″ (27) conduit or conduit fittings requires a 1 5/32″ hole. The threads per inch is 11.5 National Pipe Thread (NPT).

The standard length for most conduits is ten feet 10′ or 3.048 meters. Twenty foot 20′ (6.096 meters) lengths of metal conduit are available, but not always in stock. PVC conduit is available in ten foot 10′ and in some sizes, twenty foot 20′ lengths. RTRC mostly comes in twenty foot 20′ lengths. The flexible conduits come in various length coils and reels depending on the trade size. Some electrical supply companies will cut flexible conduit to length.

**Hole saw sizes for all electrical conduit** can be found on this post.

See my post describing various **electrical conduit types**.

**OTHER SIZE ELECTRICAL CONDUITS**

1/2″ (16) **3/4″ (21) ** 1 1/4″ (35)

1 1/2″ (41) 2″ (53) 2 1/2″ (63)

3″ (78) 3 1/2″ (91) 4″ (103)

5″ (129) 6″ (155)

**For more conduit code details and conduit fill** see Chapter 9, Tables 1, 4, 5 and 5A.

See the tables in Informative Annex C in the back of the **National Electrical Code** (NFPA 70) for the allowable number of wires in each size conduit.

## FAQs

### What is the diameter of a 1 inch conduit? ›

A conduit trade size of 1 inch has an actual inner diameter of **1.049 inches**. 2-inch lengths typically have an inside diameter of 2.067 inches.

### What is the OD of 1 electrical conduit? ›

Trade Size | Average OD (in) | Minimum Wall (in) |
---|---|---|

1/2 | 0.840 | 0.109 |

3/4 | 1.050 | 0.113 |

1 | 1.315 | 0.133 |

1-1/4 | 1.660 | 0.140 |

### What are standard conduit sizes? ›

Some typical US Customary trade sizes for conduit are **½, ¾, 1, and up to 4**. Outside the US, conduit sizes are typically measured in millimeters and are based on the outer diameter. Some common metric outer diameter sizes are 20 mm, 25 mm, 32 mm, 40 mm and 50 mm.

### What size wire can I fit in 1 inch conduit? ›

Size and Type of Conduit | 14 AWG Wire | 10 AWG Wire |
---|---|---|

1/2-inch EMT | 12 | 5 |

3/4-inch EMT | 22 | 10 |

1-inch EMT | 35 | 16 |

1 1/2-inch EMT | 84 | 38 |

### What is the diameter of conduit pipe? ›

Electrical Conduit Pipe, Size: **20 Mm, 25 Mm, 32 Mm, 50 Mm,50 Mm,20 Mm,25 Mm,32 Mm,50 Mm**.

### What is the outside diameter of 1 inch PVC conduit? ›

PVC Pipe sizes are different than the size the pipe is called. For example, a 1 inch PVC Pipe is actually **1.315 inches** in outside diameter, and 1.029 inches in inside diameter.

### What size hole do I need for 1 conduit? ›

Standard Conduit or Pipe Size (I.D.) | Actual O.D of Pipe | Actual Hole Size |
---|---|---|

3/4" | 1.050" (26.67mm) | 1.125" (28.57mm) |

1" | 1.315" (33.40mm) | 1.375" (34.92mm) |

1-1/4" | 1.660" (42.16mm) | 1.734" (44.04mm) |

1-1/2" | 1.900" (48.26mm) | 1.969" (50.01mm) |

### How do I measure conduit size? ›

Calculate the total diameter of the wires to determine the diameter of the conduit when placing wires of different gauge and type inside the conduit. Find the wire diameter in table 5 for each gauge wire and type. **Multiply the number of wires for each gauge and type by the wire diameter**. Total the results.

### What is the outside diameter of 1 inch black pipe? ›

Item # | Size | Outside Diameter |
---|---|---|

SCH 40 Pipe-1 | 1 in | 1.315 in |

SCH 40 Pipe-1 1/4 | 1 1/4 in | 1.660 in |

SCH 40 Pipe-1 1/2 | 1 1/2 in | 1.900 in |

SCH 40 Pipe-2 | 2 in | 2.375 in |

### What is the inside diameter of 1 EMT conduit? ›

Conduit Trade Size | Inside Diameter | |
---|---|---|

(in) | (mm) | (in) |

1 | 27 | 1.049 |

1 1/4 | 35 | 1.380 |

1 1/2 | 41 | 1.610 |

### Is PVC electrical conduit measured ID or OD? ›

PVC Pipe is identified by the **Inside Diameter (ID)** of the pipe. This measurement is known as 'Nominal' which means in-name-only, or a referenced name.

### Can Schedule 40 PVC be used for electrical conduit? ›

TYPES OF CANTEX PVC PIPE AND ELECTRICAL CONDUIT

Schedule 40 PVC Conduit **electrical pipe is used for electrical wiring in walls, floors and ceilings in accordance with NEC 352**. According to NEC 352 it can also be buried directly into the earth, encased in concrete, and used in areas exposed to direct sunlight.

### Where is PVC conduit not allowed? ›

PVC conduit shall not be used under the conditions specified below: (A) **Hazardous (Classified) Locations**. In hazardous (classified) locations, except as permitted by other articles of this Code. (B) Support of Luminaires (Fixtures).

### What is the wall thickness of electrical conduit? ›

Possible wall thicknesses include **“light” 2.0 mm, “medium” 2.6mm, and “heavy” 3.2mm** which implies inner diameter of 17.4mm (0.69″), 16.5mm (0.66″), 15.3mm (0.61″)

### Can you use galvanized pipe for conduit? ›

o 344.14 Dissimilar Metals.

To make this transition a stainless-steel coupling or fitting can be used in between the stainless conduit/tubing and the galvanized conduit/tubing. However, **a galvanized couplings and fittings should not be used to connect galvanized conduit/tubing to stainless steel conduit/tubing**.

### What is the size of electrical pipe? ›

PVC Electrical Conduit Pipes are available in sizes of **20mm, 25mm, 32mm, 40mm, 50mm, & 63mm** with mechanical srength of Light (LMS ), Medium(MMS), Heavy(HMS) series as per IS:9537 (Part-3) : 1983 standards. These pipes are available in standard length of 3 mtrs.

### How many 6 AWG wires can I put in a 1 inch conduit? ›

Conduit Size | Conduit Type | 6AWG |
---|---|---|

1" | EMT | 7 |

PVC | 6 | |

1-1/4" | EMT | 12 |

PVC | 11 |

### Are you allowed to run Romex in conduit? ›

When using any non metallic wire outdoor, including Romex, **it is a good idea to run it through a conduit**. Yes, they can be used outdoors, it is better to be safe than sorry. We recommend using a conduit when running the wire underground. Not only is it code, but also a good practice to ensure long life of the wire.

### What is the NEC code for conduit fill? ›

The NEC specifications are: **One wire: maximum fill is 53% of the space inside a conduit**. Two wires: maximum fill is 31% Three wires or more: maximum fill is 40% of the conduit's total available space.

### What sizes does PVC conduit come in? ›

PVC pipe can come in sizes ranging from **1/8" to 24" and larger**.

### How do you measure PVC conduit size? ›

How to measure industrial plastic pvc and abs pipe - YouTube

### Is PVC diameter inside or outside? ›

PVC Pipe is identified by the ID (**Inside Diameter**) and is referred to as a "nominal" size which means "in name only." However this confuses people and most novices try to use the OD (Outer Diameter) to order parts. If you do this, measure the OD of your pipe and find it the 2^{nd} column of the chart below.

### What is the difference between white PVC and black? ›

**ABS is always black while PVC is white**- and easy way to see the difference quickly. PVC piping offers more flexibility, but ABS is a stronger piping and can resist a higher shock. For underground, ABS is great as it can handle extreme cold and can warp if it is in direct sunlight.

### Do you measure the inside or outside of a pipe? ›

**All plastic pipe is measured on the outside diameter of the pipe, not the inside diameter**. This is because the pipe needs to fit into the socket. The pressure rating of the pipe has no significance.

### What size is a 1 inch knockout? ›

The nominal knockout diameter for 1 inch conduit is **1.375 inches**.

### What size hole saws do electricians use? ›

“The primary sizes of hole saws used by electricians are in the **2- to 7-inch range** depending on applications,” Brinson said. “Larger sizes usually are for installing recessed can lights, and sizes like the 2-inch saws are used for feeders.

### What size are knockouts? ›

Top/bottom knockouts are **2 and 1-1/2 in - sides are 2, 1-1/2, 3/4 and 1/2 in.**

### What is the outside diameter of 1 EMT conduit? ›

Electrical Metallic Conduit (EMT) Standard Stick, **1-1/4 Inch** Diameter, 10 Feet.

### Can you run 2 wires in conduit? ›

The simple answer to your question is **yes according to NEC Article 334.15 (B)**, but it may be a little more complicated than that. First the conductors must be rated for wet location. The idea is that moisture can condense in the conduit.

### How many wires can you put in a 3/4 conduit? ›

Trade Size | Wire Size (THWN, THHN) Conductor Size AWG/kcmil | |
---|---|---|

14 | ||

3/4 | EMT | 22 |

IMC | 24 | |

GRC | 22 |

### What is the outside diameter of a 1 inch pipe? ›

PIPE SCHEDULES WALL THICKNESS (Inches) | ||
---|---|---|

Nominal | O.D. Inches | 80s & E.H. |

3/4 | 1.050 | .154 |

1 | 1.315 | .179 |

1 1/4 | 1.660 | .191 |

### What are the dimensions of EMT conduit? ›

EMT is available in trade sizes **1/2 through 4, and 10′ and 20′ lengths**.

### How is EMT conduit diameter measured? ›

EMT Conduit Measurements You Need To Know - YouTube

### What is the difference between EMT and rigid conduit? ›

Electrical metallic tubing (EMT) is made from coated steel or aluminum and is a more economical and thinner-walled option than other conduit. This conduit type **doesn't offer the same protection as rigid metal conduit but is lighter and can be paired with conduit fittings, eliminating the need for threading**.

### What is the OD of 3/4 rigid conduit? ›

### How do you find the OD of a pipe? ›

**Measure the Outside Diameter (OD) of your pipe or pipe fitting:**

- Wrap a string around the pipe.
- Mark the point where the string touches together.
- Use a ruler or measuring tape to find the length between the tip of the string and the mark you made (circumference)
- Divide the circumference by 3.14159.

### What size conduit is needed for 6 3 wire? ›

You would need **2"** conduit for that.

### Is it OK to run Romex in PVC conduit? ›

**No, you can not run your Romex wiring in conduits**.

### Can I use white PVC for electrical conduit? ›

One of the biggest differences between plumbing PVC pipe (here) and PVC electrical conduit is that PVC pipes are pressure tested and PVC conduit isn't. This means that **PVC pipe and PVC conduit cannot be used interchangeably**.

### Is GREY PVC the same as white PVC? ›

There are two common types of PVC pipe – schedule 40 PVC and schedule 80 PVC. Schedule 40 PVC is usually white in color and schedule 80 is usually a dark gray (they can also be found in other colors). Their most important difference, though, is in their design. Schedule 80 pipe is designed with a thicker wall.

### Should I use metal or plastic conduit? ›

PVC conduits are also used in cases when electric wire may need to run below the ground or in an open environment that is exposed to air, dust and water. **For applications in basement or garage, where wire generally run over the surface of the wall, electrical metal conduits are best**.

### Can I run PVC conduit above ground? ›

Among all conduit types, PVC is lightweight and versatile. Available in a variety of thicknesses or grades, **PVC is well suited for direct burial or above ground work**. PVC conduit is also used for many electrical requirements. This product is flexible and durable and resists corrosion.

### Why is PVC not allowed in homes? ›

The reason for not allowing PVC for distribution pipe is that **it is not rated to withstand the thermal expansion stress caused by hot water**. Even cold water pipe inside a home can end up with hot water in it, because the heat inside a water heater transfers backward through the water in the cold water supply pipe.

### What is the outside diameter of 1 inch electrical conduit? ›

Nominal Conduit Size Inches | Nominal Conduit Size mm | Conduit Outside Diameter Inches |
---|---|---|

1" | 27 | 1.163 |

1-1/4" | 35 | 1.510 |

1-1/2" | 41 | 1.740 |

2" | 53 | 2.197 |

### What is the standard rigid conduit size? ›

RMC is available in trade sizes **1/2 through 6, and 10′ and 20′ lengths**. RMC is threaded on both ends, with a coupling applied to one and a color-coded thread protector on the other.

### What is the minimum size rigid electrical conduit? ›

Trade Size | Average OD (in) | Minimum Average ID (in) |
---|---|---|

4 | 4.500 | 3.961 |

5 | 5.563 | 4.975 |

6 | 6.625 | 5.986 |

8* | 8.625 | 7.853 |

### Can you use black iron for electrical conduit? ›

TLDR; **Iron heating pipe is not approved for use with electrical conductors or as sleeves in long runs**. Not Advisable.

### Can black pipe be used as electrical conduit? ›

Black steel pipes have a variety of use thanks to their strength and needs for little maintenance. They tend to be used for transporting gas and water to rural areas and urban areas or **for conduits that protect electrical wiring** and deliver high pressure steam and air.

### What thread is electrical conduit? ›

The pitch of conduit threads conforms to the American National Standard for Pipe Threads, General Purpose (Inch), ANSI/ASME B1. 20.1. The taper of threads is **3/4 inch per foot (1 in 16)**.

### What is the outside diameter of 1 inch PVC conduit? ›

PVC Pipe sizes are different than the size the pipe is called. For example, a 1 inch PVC Pipe is actually **1.315 inches** in outside diameter, and 1.029 inches in inside diameter.

### Is conduit measured by ID or OD? ›

Tubing is measured by the **OUTSIDE DIAMETER (O.D.)**, specified in inches (e.g., 1.250) or fraction of an inch (eg. 1-1/4″). Pipe is usually measured by NOMINAL PIPE SIZE (NPS). Although it is related to the outside diameter, it is significantly different.

### How do you measure electrical conduit size? ›

Calculate the total diameter of the wires to determine the diameter of the conduit when placing wires of different gauge and type inside the conduit. **Find the wire diameter in table 5 for each gauge wire and type.** **Multiply the number of wires for each gauge and type by the wire diameter**. Total the results.

### What is the inside diameter of 1 inch EMT conduit? ›

A: The nominal inside diameter is 1/2 inch. The nominal outside diameter is 7/8 inch.

### How is conduit diameter measured? ›

Tubing is measured **by the OUTSIDE DIAMETER (O.D.), specified in inches (e.g., 1.250) or fraction of an inch (eg.** **1-1/4″)**. Pipe is usually measured by NOMINAL PIPE SIZE (NPS). Although it is related to the outside diameter, it is significantly different.

### How do you measure electrical conduit diameter? ›

EMT Conduit Measurements You Need To Know - YouTube

### Is PVC conduit measured ID or OD? ›

PVC Pipe is identified by the **Inside Diameter (ID)** of the pipe.

### What is the outside diameter of 1 inch black pipe? ›

Item # | Size | Outside Diameter |
---|---|---|

SCH 40 Pipe-1 | 1 in | 1.315 in |

SCH 40 Pipe-1 1/4 | 1 1/4 in | 1.660 in |

SCH 40 Pipe-1 1/2 | 1 1/2 in | 1.900 in |

SCH 40 Pipe-2 | 2 in | 2.375 in |

### What are the dimensions of EMT conduit? ›

EMT is available in trade sizes **1/2 through 4, and 10′ and 20′ lengths**.

### What is the wall thickness of conduit? ›

Possible wall thicknesses include **“light” 2.0 mm, “medium” 2.6mm, and “heavy” 3.2mm** which implies inner diameter of 17.4mm (0.69″), 16.5mm (0.66″), 15.3mm (0.61″)

### What is the outside diameter of a 1 inch pipe? ›

PIPE SCHEDULES WALL THICKNESS (Inches) | ||
---|---|---|

Nominal | O.D. Inches | 80s & E.H. |

3/4 | 1.050 | .154 |

1 | 1.315 | .179 |

1 1/4 | 1.660 | .191 |

### Is pipe diameter inside or outside? ›

In short: Tube is measured by outside diameter, pipe is measured by **inside diameter**. There is often confusion as to which size die the customer actually needs - Pipe Size or Tubing Size. Keep in mind that pipe size refers to a nominal - not actual - inside pipe diameter. Schedule refers to the pipe's wall thickness.

### How is PVC electrical conduit measured? ›

PVC Pipe sizes are so named **by the measurement of the inside diameter (also called the bore) of the PVC pipe**, and not the outside diameter. If you measure the outside diameter it will give you a larger reading than the actual PVC Pipe Size.

### What is the size of electrical pipe? ›

PVC Electrical Conduit Pipes are available in sizes of **20mm, 25mm, 32mm, 40mm, 50mm, & 63mm** with mechanical srength of Light (LMS ), Medium(MMS), Heavy(HMS) series as per IS:9537 (Part-3) : 1983 standards. These pipes are available in standard length of 3 mtrs.

### Does ground wire count in conduit fill? ›

Moderator. **If the EGC is in the pipe it counts as fill**.

### What is the difference between white PVC and black? ›

**ABS is always black while PVC is white**- and easy way to see the difference quickly. PVC piping offers more flexibility, but ABS is a stronger piping and can resist a higher shock. For underground, ABS is great as it can handle extreme cold and can warp if it is in direct sunlight.

### What is the outside diameter of 1 EMT conduit? ›

Electrical Metallic Conduit (EMT) Standard Stick, **1-1/4 Inch** Diameter, 10 Feet.

### Is PVC pipe diameter inside or outside? ›

PVC Pipe is identified by the ID (**Inside Diameter**) and is referred to as a "nominal" size which means "in name only." However this confuses people and most novices try to use the OD (Outer Diameter) to order parts.