Sized from 1/4" to 1", we've got the size you need. A clamp is included. Caps are sold individually--select quantity to get the number you need!
Boost & Pressure Rated: The multi-ply fabric reinforcement prevents the cap from stretching or bursting, making it safe for high-pressure cooling systems and forced induction vacuum ports.
Extreme Temperature Resistance: Built to withstand constant under-hood temperatures from -65°F to +350°F—ideal for turbocharger and supercharger applications.
No-Slip Interior Lining: Special liner provides a superior grip on metal bungs, preventing "blow-offs" under high boost or cooling system spikes.
UV & Ozone Resistant: The high-gloss black finish won't dry out, crack, or fade, ensuring your engine bay looks as good as it performs for years to come.
Clamp-Ready Durability: Specifically designed to withstand the high clamping force of T-bolt or worm-gear clamps without tearing or collapsing the sidewall.
Choosing the right size is critical for a leak-proof seal. Our caps are measured by their Inside Diameter (I.D.). To find your match, you must measure the Outside Diameter (O.D.) of the fitting you intend to cap.
Measure the Fitting: Use a digital caliper to measure the Outside Diameter (O.D.) of the barb or threaded port you are capping.
Match the I.D.: Select the cap with an Inside Diameter (I.D.) that matches your fitting's O.D.
Example: A 5/8" (16mm) heater hose barb requires a 5/8" I.D. silicone cap.
The "Snug" Rule: If your measurement falls between sizes, always choose the smaller size for a snug fit, as silicone can stretch slightly (up to 5%) to create a tight seal.
ALL CAPS MUST BE SECURED WITH A CLAMP!
| I.D. Size (Inches) | Metric Equiv. | Common Application |
| 1/8" | 3mm | Small vacuum ports, boost controllers, MAP sensors. |
| 3/16" | 5mm | Standard vacuum lines, windshield washer ports. |
| 1/4" | 6mm | Large vacuum bungs, fuel pressure regulators. |
| 5/16" | 8mm | Fuel rail returns, larger vacuum ports, and vapor canisters. |
| 3/8" | 10mm | PCV ports, small coolant bypass lines. |
| 7/16" | 11mm | European coolant expansion tanks and specialized bypass ports. |
| 1/2" | 13mm | Intake manifold bungs, throttle body coolant ports. |
| 5/8" | 16mm | Most Common: Standard heater core delete/bypass. |
| 3/4" | 19mm | Large heater hose ports, water pump bypasses. |
| 1.0" | 25mm | Radiator overflow, large custom coolant crossovers. |
| Feature | Rating / Detail |
| Material | 4-Ply High-Temp Reinforced Silicone |
| Temperature Range | -54°C to +177°C (-65°F to +350°F) |
| Max Pressure | Up to 100 PSI (size dependent) |
| Compatibility | Coolant, Water, Air, Vacuum, Boost |
| Visuals | High-Gloss Black with Black Inner Core |