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Finish Line Factory technical library
NPT connections use tapered pipe threads. The size is nominal: 1/4-inch NPT is not a 1/4-inch measured outside diameter. AN flare threads are straight and seal at the seat; NPT seals through the threaded joint.
On small screens, scroll the table sideways to see all columns.
| Nominal pipe size (in) | Threads/in | Published overall length (in) | Nominal pipe OD (in) | Tap drill (in) |
|---|---|---|---|---|
| 1/16 | 27 | 0.3896 | 0.313 | 15/64 |
| 1/8 | 27 | 0.3924 | 0.405 | 21/64 |
| 1/4 | 18 | 0.5946 | 0.540 | 7/16 |
| 3/8 | 18 | 0.6006 | 0.675 | 37/64 |
| 1/2 | 14 | 0.7815 | 0.840 | 23/32 |
| 3/4 | 14 | 0.7935 | 1.050 | 59/64 |
| 1 | 11-1/2 | 0.9845 | 1.315 | 1-5/32 |
Before ordering
Measure diameter and pitch, then identify taper and sealing design. NPS straight pipe threads, ORB and BSP connections require their own matching interfaces. Do not choose an adapter from diameter alone.
NPT taper is 3/4 inch per foot. Select sealant and installation procedure for the exact fitting and fluid. Keep sealant out of the fluid path. The drill dimensions are references, not a complete machining procedure.
Continue with AN identification or shop thread adapters and weld bungs.
Shop & get help
Shop Finish Line Factory · Ask Lee Motorsports about your setup
Technical reference: FLF Racing Supply / Finish Line Factory. Checked October 6, 2026. Use the instructions for your exact components.