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HornBlasters train horn kit installed under a vehicle

Help Center · Fittings

NPT Threads

NPT sizes do not match a simple tape-measure reading. Use the OD chart below to identify male pipe threads.

  • What you need: tape measure or calipers for outside diameter

Overview

1

Why a “1/4" NPT” does not measure 1/4"

Pipe thread sizing is based on nominal pipe size, not the OD you measure with a tape. A 1/4" NPT male thread measures about 0.540" across the outside of the threads — which confuses most people the first time they check.

This chart helps you match a fitting or port to the correct NPT size.

Determining Thread Size

2

Male NPT outside diameter chart

With a standard tape measure, a 1/4" NPT fitting should read about 0.540". Use the chart for male pipe threads; female threads measure slightly different but are close.

Pipe size Outside diameter Threads per inch
1/8" NPT 0.405" 27
1/4" NPT 0.540" 18
3/8" NPT 0.675" 18
1/2" NPT 0.840" 14
3/4" NPT 1.050" 14

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Connect Ford Upfitter Switches to your HornBlasters kit — wiring locations, fuses, and year-by-year switch notes.

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