Imperial Thread Chart for Imperial Bolt Sizes.

⇩ SCROLL TO IMPERIAL SIZE CHART ⇩

Imperial bolt sizes are manufactured according to specific imperial thread dimensions and specifications, often governed by standards such as the Unified Thread Standard (UTS) in the United States. These standards ensure compatibility between mating components, much like metric threads. The imperial size chart below represents the dimensions of common coarse (UNC), fine (UNF) and extra fine (UNEF) imperial common bolt thread sizes.

Please note that these figures relate to product design and should always be implemented with thread tolerances in mind. In practice, values related to tapping and drilling can vary depending on factors such as material properties and operating temperature. Use these imperial thread dimensions as a guide and perform a test fit on a scrap workpiece if you’re uncertain. Measure twice, tap once.

To see imperial thread sizes in mm, take a look at our metric-to-imperial conversion chart. If you need metric sizing, then our metric screw size chart has everything you need. 

Imperial Thread Sizes Chart & Imperial Bolt Dimensions.

Upgrade Your Workshop with Our Printable Imperial Screw Thread Chart.

Maximise efficiency and precision in your engineering projects with our indispensable imperial screw size chart. Designed for professionals who demand accuracy, this downloadable poster offers detailed insights into imperial thread dimensions for bolts and screws alike.

Printing and placing these charts in your workshop ensures that the specifications you need are always within reach. Elevate the standard of your projects and streamline your workflow with this essential imperial screw-size resource.

Imperial Screw Thread Sizes Explained.

In our imperial screw thread size chart above, dimensions are denoted by a series of numbers and letters that encapsulate various dimensions including the major diameter, threads per inch (TPI) and thread type. Common designations like 1/4-20 UNC signify a screw with a 1/4 inch major diameter and 20 threads per inch, following the Unified National Coarse (UNC) standard. This naming convention of imperial-size screws enables engineers to swiftly identify and match threaded components, thereby facilitating streamlined procurement and assembly processes.

Major Diameter (Inches) Explained.

The major diameter in our imperial thread dimensions chart, measured in inches, refers to the largest diameter of a threaded shank. It is measured across the crests of the threads. Precise measurements can be acquired using vernier calipers. This is a critical parameter as it essentially dictates all imperial bolt sizes.

Minor Diameter (Inches) Explained.

The minor diameter in our imperial thread chart is the smallest diameter of a threaded element, often referred to as the root of the thread. This dimension is measured across the roots of the threads and is crucial for indicating the quality and strength of the thread.

Threads Per Inch (TPI) Explained.

The TPI column in our imperial thread pitch chart refers to the number of threads per inch along the length of the screw or bolt. This is a crucial measurement affecting the thread’s mechanical properties and compatibility with mating components. Special instruments like thread gauges are commonly used to measure this attribute.

Tapping Drill Diameter (Inches) Explained.

The tapping drill diameter is the diameter of the drill hole required before the tapping process can begin. This parameter is closely aligned with the minor diameter and typically varies based on material properties and application requirements. Accurate measurement post-tapping ensures that the threads achieve the desired fit and strength.

Clearance Hole Diameter (Inches) Explained.

The clearance hole diameter in our imperial thread size chart is the diameter of the hole that allows a bolt or screw to pass through without engaging the threads. This is crucial for ensuring easy assembly and disassembly. The diameter is generally measured using calipers and should be chosen based on the bolt’s major diameter plus an additional margin for ease of fit.

FAQs

Q: What does imperial thread sizes mean?

A: Imperial thread size refers to the system of measurements used for screws, bolts and other threaded components based on inches. These sizes include specifications like diameter, threads per inch (TPI) and pitch.

Q: How to read imperial thread size?

A: Imperial thread sizes are typically displayed as a fraction or decimal (e.g. 1/4") for the diameter, followed by the threads per inch (TPI) and sometimes a classification like UNC (Unified National Coarse) or UNF (Unified National Fine), e.g. 1/4-20 UNC.

Q: Are metric and imperial threads the same?

A: No, metric and imperial threads are not the same. Metric threads are measured in millimetres and use a different standard for pitch and diameter, while imperial threads are measured in inches with TPI.

Q: Is BSP thread imperial?

A: Yes, BSP (British Standard Pipe) threads are considered imperial as they are measured in inches. However, they are specifically used for pipe fittings and have their own distinct thread profile and standards.