1/8 NPT & 3/8 NPT Protective Caps (Male & Female)

This set includes both Male and Female protective caps for the two most common small pipe sizes in automotive and industrial plumbing: 1/8 NPT and 3/8 NPT.

These are perfect for sealing off ports on turbochargers, oil sandwich plates, fuel rails, or intake manifolds while your engine is being built or stored.

📐 Understanding NPT (Why they don't screw in all the way)

If you are used to standard bolts (Metric or AN), you might be surprised when these caps stop after only a few turns. This is normal.

Unlike "straight" threads, NPT (National Pipe Taper) threads are cut on a 1.789° taper.

• The Wedge Effect: As you screw the male end into the female end, the diameter of the male part increases while the female part decreases.
• Engagement: In real steel fittings, you typically get about 3 to 4.5 threads of hand-tight engagement before the threads "wedge" together to create a seal.
• The Caps: These 3D-printed caps mimic this taper. Do not force them. They are designed to sit snugly after a few turns to keep dust out.

🛠️ Print Settings

• Material: PETG is recommended for better chemical resistance to oil/fuel residues and better thread flexibility.
• Layer Height: 0.15mm (High detail is essential for the tapered NPT threads to function correctly).
• Infill: 20% is plenty for a dust cap.
• Walls: 3 wall lines.
• Supports: None needed.

⚠️ Disclaimer

These are DUST CAPS ONLY. Because NPT relies on metal-to-metal deformation and sealant (Teflon tape) for a high-pressure seal, these plastic prints should NEVER be used in a pressurized system or on a running engine.