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Threads

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Threads

The tables and articles in this chapter help you correctly identify inch-based threads used on Harley-Davidson motorcycles and compare them with their metric equivalents. They include information on tap drill diameters for internal threads, small thread sizes in the SAE numbering system, as well as SAE pipe threads. This allows you to correctly select and install fasteners and components.

Core Drill Diameters for Internal Threads

Core Drill Diameters for Internal Threads

The table lists SAE threads (A) and their respective core drills in SAE measures (B) and in mm (C).

Small Thread Sizes - SAE Number System to Metric

Small Thread Sizes - SAE Number System to Metric

Screws with thread diameters smaller than 1/4” are not denoted with fractional numbers but follow the SAE number system. Example: size denotation 10-24. The number 10 describes the diameter which is 4.8 mm according to the chart. The number 24 regularly indicates threads per inch.

NPT Threads on Tube Connectors

NPT Threads on Tube Connectors

Thread particulars for tube connectors most often contain three letters: NPT. NPT stands for National Pipe Thread. In contrary to other threads, the fractional number before the dash has little to do with theactual diameter, and - what's more - on a keen inspection of the thread you'll see that it is conical. For your convenience follows a table of the most common pipe threads on Harleys: