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CD-6 – Caplugs Red Threaded Cap
Part Number: CD-6
Manufacturer: Caplugs
Standard Series: CD (Threaded Caps for Flared JIC Fittings)
NSN: 5340-00-392-7334 / 5340-00-664-0671
Overview Section
The CD-6 is a high-visibility red threaded plastic cap designed specifically to protect 3/8" flared JIC (Joint Industry Council) hydraulic and fuel fittings. Part of the industry-standard CD Series by Caplugs, this component acts as a rugged barrier against dirt, moisture, and mechanical damage during transit, storage, or maintenance.
Constructed from Low-Density Polyethylene (LDPE), the CD-6 provides a snug, reliable seal on external threads. Its knurled exterior ensures ease of manual application and removal, making it a staple for aviation technicians, hydraulic engineers, and MRO facilities worldwide.
Enhanced Technical Data
| Technical Metric | Specification Data |
| Material Base | Low-Density Polyethylene (LDPE) |
| To Fit Nominal Tube Size | 3/8 in |
| To Fit Thread Size | 9/16 – 18 (Unified Fine Thread) |
| JIC Fitting Dash Size | -6 |
| Height (Dim A) | 0.53 in (13.46 mm) |
| Service Temperature | $-94°F$ to $175°F$ ($-70°C$ to $79°C$) |
| Exterior Grip | 6 Knurls for manual torque |
| Chemical Resistance | Resistant to common hydraulic fluids, fuels, and acids |
Advanced Engineering & Structural Application
The CD-6 is engineered for Environmental Isolation. In the aviation and hydraulic industries, open lines are the primary source of system contamination. The CD-6 features a precision-molded internal thread that maintains a positive seal, preventing foreign object debris (FOD) from entering critical fluid systems.
Engineering Insight: Masking and Protection
While primarily a protective cap, the CD-6 is frequently utilized as a Masking Solution during painting, plating, or powder-coating operations. Its LDPE composition resists the chemicals found in many aviation primers and topcoats. Furthermore, the material's specific Shore D Hardness (41–46) allows it to absorb impacts without cracking, which is vital for protecting the delicate 37° flare sealing surface of JIC fittings.
Aircraft Compatibility & Industry Use
The CD-6 is found in almost every aircraft maintenance hangar and is compliant with several aerospace standards:
Aviation MRO: Standard protection for fuel, hydraulic, and oil lines on Cessna, Beechcraft, and Piper aircraft.
Hydraulic Systems: Used for protecting pump outlets, manifold ports, and flexible hose ends.
Military/Defense: Cross-referenced with NAS 832 and NAS 833 specifications for protective covers.
Industrial Manufacturing: Preferred for heavy machinery and automotive hydraulic assembly.
The Caplugs CD-6 is the professional’s choice for sealing and protecting 3/8" JIC fittings. Whether you are performing a hydraulic system overhaul or preparing an engine for shipment, the CD-6 ensures that your threads and flared surfaces remain factory-clean. Its rugged LDPE construction and ergonomic knurled design make it superior to unthreaded push-on caps that can vibrated loose. For aerospace and defense applications requiring NSN 5340-00-392-7334, the CD-6 provides cost-effective, military-grade protection that withstands the harsh environments of the flight line.
Installation & Maintenance Addendum
Hand Tighten Only: The CD-6 is designed for manual application. Excessive torque with tools may strip the plastic threads or make removal difficult.
Cleanliness Check: Before installing the cap on a critical fluid line, ensure the internal threads of the CD-6 are free of plastic burrs or dust.
Reuse Policy: While durable, LDPE caps should be inspected for thread wear if reused. For sensitive hydraulic systems, it is recommended to use a new cap to ensure zero contaminant transfer.
