1.5″ Pool Fitting Thread Fit-Test Set - BSPP, BSPT & NPT

Check the thread before ordering your pool lights

Not sure whether your pool fitting uses BSP or NPT threads? This set contains three externally threaded samples for comparing the fit in an internally threaded, nominal 1½-inch pool fitting.

The set includes BSPP (parallel BSP), BSPT (tapered BSP), and NPT (tapered American pipe thread). Each sample is clearly labeled so you can keep track of which version you are testing.

These models are intended to help narrow down the likely thread type before ordering pool lights or other compatible components. They are temporary fit-test samples—not functional plugs, seals, light mounts, or calibrated thread gauges.

Dimensions and features

Each model is 40 mm tall overall, consisting of a 20 mm threaded section and a 20 mm finger grip. The grip has a maximum diameter of 56 mm, with shallow scallops for turning by hand and a 5 mm transverse hole for a retrieval cord.

A chamfered thread entry helps with starting the sample. The top face carries engraved identification showing the thread family, nominal size, TEST, and C0.2.

The supplied threads have a 0.20 mm reduction in diameter—0.10 mm per side—as a printing allowance. This is what C0.2 refers to; it is not a guaranteed clearance or a tolerance certification. Thread pitch is unchanged.

The 40 mm dimension is the complete model height, not the available insertion depth.

Suggested print settings

Print in millimetres at 100% scale, with the large flat grip face on the build plate and the threaded end pointing upward. The slicer should show an overall size of 56 × 56 × 40 mm.

For a 0.4 mm nozzle, suggested starting settings are 0.15 mm layers, 3–4 walls, 15–20% infill, and at least 4 top/bottom layers. Start with supports disabled, and inspect the sliced threads and retrieval-cord hole before printing.

PLA is a suggested starting material for a brief, attended fit test. Use the same material and settings for all three samples to make the comparison more meaningful. These settings have not been physically validated.

Do not resize the models to match the measured opening diameter: scaling changes the thread pitch as well as the diameter. The nominal 1½-inch designation is not the measured outside diameter.

Testing and limitations

Attach a retrieval cord and test with the pool pump switched off. Isolate any relevant lighting circuit before working at a light fitting. Do not disturb existing plumbing or electrical seals.

Try BSPP first, then BSPT and NPT separately. Start each sample squarely and use fingertip pressure only. Smooth engagement over several turns is more useful than simply catching the first thread. Stop at resistance; do not use tools, tape, or sealant, and do not force the grip against the fitting.

Remove each sample immediately after testing. Never leave a sample installed, run the pump with one fitted, or use one to retain water.