DESCRIPTION
The Blu-Sub UNF Sealing Plug (Blank) is a high-integrity sealing solution designed to close off unused UNF-threaded ports in underwater equipment. These plugs are especially useful when preparing modular builds or reserving ports for future upgrades involving Subconn-style or other UNF-format connectors. Each unit includes a plug, O-ring, stainless steel washer, and nut to ensure a pressure-rated, watertight seal rated for depths up to 1,000 m (3,280 ft).
The UNF plug comes in two mechanical styles: standard hex-head (with internal wrench socket) and square-format. Both versions are engineered for secure installation and long-term performance in subsea environments. Brown fluorine rubber O-rings are used as standard for durability across a wide temperature range, supporting service lifetimes up to 3 years or 500 install/remove cycles depending on conditions.
Thread sizes include 7/16-20, 1/2-20, 5/8-18, and 3/4-16 UNF, covering most common port sizes found on underwater connector panels and bulkheads. The aluminum version is anodized black for corrosion resistance and visual consistency with other Blu-Sub components; the stainless steel version retains its natural finish.
These UNF sealing plugs are functionally equivalent to the Metric Sealing Plug (Blank), which is available in M6, M8, M10, M14, and M16 thread sizes. While the Metric version is tailored to standard Blu-Sub endcaps and tubes, the UNF version is intended for compatibility with third-party panels and devices using Unified National Fine threads.
Both plug types enable watertight closure of unused penetrator ports to protect internal electronics, simplify routing, and support scalable system design. This is especially valuable when building ROVs, underwater sensor modules, or testing platforms where full connector populations are not yet required. Maintaining unused port integrity is essential for ensuring consistent enclosure pressure balance and long-term reliability.
All plugs are supplied with high-quality sealing hardware and are compatible with standard installation tools. Note: While small internal air gaps or pressure differentials may develop behind unused plugs during rapid submersion or decompression, this does not affect sealing performance under normal operating conditions.
Also Available: Metric Sealing Plugs (Blank)
Sold Separately
Also available as the Metric Sealing Plug (Blank) for standard thread sizes like M6, M8, M10, M14, and M16. These metric plugs offer the same watertight performance and are designed to fit Blu-Sub end caps and enclosure tubes with metric ports.
SHIPPING LIST
TECHNICAL SPECIFICATIONS
| Item | UNF Sealing Plug (Blank) |
| Material |
316 Stainless Steel (Also available in 6061 Aluminum for 7/16-20 Plug) |
| Appearance |
Original Stainless Steel Color (Black Anodized for 7/16-20 Aluminum) |
| O-ring Size |
7/16-20 Plug (Stainless or Aluminum): Ø12.42 × 1.78 1/2-20 Plug: Ø14 × 1.78 5/8-18 Plug: Ø17.2 × 1.78 3/4-16 Plug: Ø21.95 × 1.78 Square FCR1500 Plug: Ø19 × 2.5 + Ø13 × 1.5 Square FCR2000 Plug: Ø22.22 × 2.62 + Ø15.6 × 1.78 |
| O-ring Material | FKM75 Brown Fluorine Rubber |
| Maximum Rated Depth | 1,000 m / 3,280 ft |
| Design Lifetime | Up to 3 years or 500 cycles |
| Temperature Rating (Air) | –25 ~ 60 °C / –13 ~ 140 °F |
| Temperature Rating (Water) | –4 ~ 40 °C / 32 ~ 104 °F |
| Internal Hex Socket | 6 mm (opposite sides) for bolt-type plugs; not applicable to square-type plugs |
Attention: The hex socket on the top is designed only for quick tightening or loosening. It is not suitable for applying high torque. To achieve proper installation torque, use a suitable wrench to tighten the flat sides of the bulkhead.
Dimensions Referencing Drawing A
| Size | 7/16-20 Plug | 1/2-20 Plug | 5/8-18 Plug | 3/4-16 Plug | Square FCR1500 Plug | Square FCR2000 Plug |
| Thread Size / Shaft Diameter (A) | 7/16-20UNF-2A | 1/2-20UNF-2A | 5/8-18UNF-2A | 3/4-16UNF-2A | 15.9 (–0.016 / –0.034) | 18.8 (–0.02 / –0.041) |
| Distance Across Flats (B) | ¾″ (19.05) | 13⁄16″ (20.64) | 1″ (25.4) | 1-3⁄16″ (30.16) | – | – |
| Assembled Height from Endcap (C) | 9 | 9 | 9 | 9 | 8.2 | 9.5 |
| Thread Length / Shaft Length (D) | 20 | 20 | 20 | 20 | 12.7 | 12.7 |
| Overall Outer Diameter / Width (E) | 21.6 | 23.4 | 28.8 | 34 | 38.1 | 44.4 |
| Wrench Socket Height (F) | 7.5 | 7.5 | 7.5 | 7.5 | – | – |
| Installation Location (G) | – | – | – | – | 35.92 | 44.9 |
Dimensions Referencing Drawing B
| Size | 7/16-20 Plug | 1/2-20 Plug | 5/8-18 Plug | 3/4-16 Plug | Square FCR1500 Plug | Square FCR2000 Plug |
| Hole Size (A, d) | Ø0.445″ (11.3 ± 0.1) | Ø0.504″ (12.8 ± 0.1) | Ø0.629″ (16 ± 0.1) | Ø0.807″ (20.5 ± 0.1) | Ø15.9 (+0.027 / 0) | Ø18.8 (+0.033 / 0) |
| Hatch Cover Thickness (B) | – | – | – | – | 13 | 13 |
| Surface Range (D) | 25 | 25 | 30 | 40 | 50 | 60 |
Dimensions Referencing Drawing C
| Size | 7/16-20 Plug | 1/2-20 Plug | 5/8-18 Plug | 3/4-16 Plug |
| Nut Height (A) | 6.5 | 8 | 9.5 | 10.5 |
| Maximum OD of Nut (B) | 20 | 21.5 | 27 | 32 |
| Nut across Flats (C) | 11/16″ | 3/4″ | 15/16″ | 1-1/8″ |
| Washer Outer Diameter (D) | 23.6 | 27 | 33.5 | 38 |
| Washer Inner Diameter (E) | 12 | 13.5 | 17 | 21 |
| Washer Thickness (F) | 1.4 | 2 | 2 | 3 |
Dimension Drawing A
Dimension Drawing B
Dimension Drawing C
Can I reuse the UNF blank plug multiple times?
Yes, the plug is designed for up to 500 installation/removal cycles over a service life of approximately 3 years. Always inspect the O-ring before reuse to ensure proper sealing.
Is the plug compatible with Subconn or other UNF ports?
Yes, it is compatible with Subconn blank plug ports that use British-standard UNF threading.
What tool should I use to install or remove the plug?
Use a hex wrench for the internal socket during initial tightening or removal. For final tightening, apply torque using an appropriate wrench across the flat sides of the hex base.
Will water leak if the O-ring contact surface is scratched?
Yes, any scratch or damage to the O-ring seat may compromise waterproofing. Always inspect mating surfaces and replace damaged plugs or O-rings.
Is the square-type plug interchangeable with the bolt-type plug?
No, square-type and bolt-type plugs have different dimensions and are not interchangeable. Select the correct plug type for your enclosure design.
Can I use this plug above water or only underwater?
The plug is rated for both air and water environments with temperature ranges from -25 °C to 60 °C in air, and -4 °C to 40 °C in water. It can be used in both environments as long as proper sealing is maintained.
3D Model Viewer
Note: The 3D model shown above is for reference purposes only. It may include components, accessories, or alternate sizes not included with the product. For simplicity, only a single representative size is typically displayed when multiple versions exist. Please refer to the product Shipping Guide for detailed information on included contents and size-specific differences.
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