TES-LOK Hex Plug Tube Fittings — solid male external thread with hexagonal head, seals and blanks open female-threaded ports completely. Dead-end blanking, spare port sealing, vent/drain closure, and test connection capping in instrument and process assemblies. SS 316 · Brass · Monel · Inconel · NPT · BSPT · BSPP · 1/16"–2" · Up to 6,000 PSI · ISO 9001:2015 certified.
A hex plug is a solid male-threaded fitting with a hexagonal head used to blank off and permanently seal open female-threaded ports. Unlike a nipple, union, or adapter which has a through-bore, the hex plug has a completely solid body — there is no bore, no flow path, and no opening through the fitting. When threaded into a female port, the plug converts that port into a closed dead end, preventing any fluid from entering or exiting.
The hexagonal head sits proud of the port face after installation, providing a wrench flat surface that allows the plug to be tightened to the correct torque and later removed for port access using a standard open-end or combination wrench — without damaging the port body or requiring a pipe wrench. TES-LOK hex plugs are precision-machined to ASME B1.20.1 (NPT), BS EN 10226 (BSPT), and BS EN ISO 228-1 (BSPP) thread standards, ensuring full thread engagement and consistent sealing performance in every female port they enter.
| Fitting | Thread | Body | Seals | Use When |
|---|---|---|---|---|
| Hex Plug | Male external | Solid hex head | Female-threaded port (socket) | The port to be blanked is a female thread — the plug screws in |
| Hex Cap | Female internal | Solid hex head | Male-threaded nipple or stud | The component to be capped is a male thread — the cap screws on |
| Tube Cap | None — compression | Solid body | Open tube end (compression) | The end to be blanked is an open tube — the cap bites onto the tube OD |
| Blind Flange | None — bolted | Solid disc | Flanged pipe end | The opening to be blanked is a flanged pipe end — large bore, high-pressure class |
| Thread Form | Standard | Seal Method | Common Port Type |
|---|---|---|---|
| NPT (Male) | ASME B1.20.1 | PTFE tape on plug thread (2–3 wraps) | US-standard instrument valves, manifolds, gauge ports, US process equipment |
| BSPT (Male) | BS EN 10226 | PTFE tape on plug thread (2–3 wraps) | UK/European instrument equipment with tapered BSP female ports |
| BSPP (Male) | BS EN ISO 228-1 | Dowty bonded seal on plug shoulder | Hydraulic and pneumatic manifolds, European process equipment with parallel BSP ports |
| Thread Form | Male NPT (ASME B1.20.1); Male BSPT (BS EN 10226); Male BSPP (BS EN ISO 228-1) |
| Thread Size Range | 1/16" to 2" — all standard instrument and process pipe sizes |
| Head Form | Hexagonal (hex) — full hex head for open-end wrench engagement |
| Body | Solid — no bore, no through-hole, complete port blanking |
| Working Pressure | Up to 6,000 PSI (SS 316, ambient); 3,000 PSI (Brass) |
| Standard Material | SS 316 (ASTM A276 / A479) |
| Optional Materials | SS 316L, SS 304, Brass (CW617N), Monel 400, Inconel 600, Hastelloy C-276 |
| Surface Finish | Bright annealed or passivated (SS); natural (Brass); electroless nickel plating on request |
| Temperature Range | -196°C to +450°C (SS 316); -10°C to +120°C (Brass) |
| Thread Gauging | GO/NO-GO thread gauge check per applicable standard before despatch |
| Quality Certification | ISO 9001:2015; EN 10204 3.1 MTCs available; PMI testing on request |
| Thread Size | NPT | BSPT | BSPP | Typical Blanking Application |
|---|---|---|---|---|
| 1/16" | ✓ | ✓ | ✓ | Miniature instrument vent ports; micro-bore gauge connections |
| 1/8" | ✓ | ✓ | ✓ | Small gauge and transducer spare ports; instrument case drain plugs |
| 1/4" | ✓ | ✓ | ✓ | Instrument manifold spare ports; pressure gauge isolation valve test connections |
| 3/8" | ✓ | ✓ | ✓ | Flow meter spare ports; valve body drain connections during normal service |
| 1/2" | ✓ | ✓ | ✓ | Process manifold spare ports; valve body vent connections; condensate pot drain plugs |
| 3/4" | ✓ | ✓ | ✓ | Valve body drain plugs; pump casing instrument port blanks; heat exchanger drain connections |
| 1" | ✓ | ✓ | ✓ | Main process valve drain plugs; large manifold block spare ports; pipe drain points |
| 1-1/4" | ✓ | ✓ | ✓ | Industrial valve body blanking; large-bore instrument nozzle spare ports |
| 1-1/2" | ✓ | ✓ | ✓ | Tank drain port blanking; large valve body test connections |
| 2" | ✓ | ✓ | ✓ | Main process line drain plugs; large industrial valve body spare ports |
| Plug Thread Form | Sealant Required | Application Notes |
|---|---|---|
| NPT Male Plug | PTFE tape (2–3 wraps clockwise) or anaerobic thread sealant on plug thread | Taper-seal thread — thread deforms as plug advances into female port. Hand-tight plus 2–3 turns. Do not over-torque — can crack female port on aluminium or brass bodies. |
| BSPT Male Plug | PTFE tape (2–3 wraps clockwise) on plug thread | Same taper-seal principle as NPT. BSPT and NPT are NOT interchangeable — different pitch (BSPT: 55°; NPT: 60°). Do not mix. |
| BSPP Male Plug | Dowty bonded seal on plug shoulder | Parallel thread — no taper seal. Dowty washer between plug shoulder and port face provides seal. No PTFE tape. Tighten until Dowty washer is fully compressed flat. |
The solid hex plug body contains no bore whatsoever — there is no path for fluid to pass through, no hidden cavity that could trap process fluid, and no internal surface that could corrode from the inside. When a hex plug is installed and properly sealed, the port it seals is as closed as the surrounding body material. This makes hex plugs the correct choice for permanent port blanking, dead-end sealing, and safety-critical spare port closure on pressure vessels, manifolds, and instrument assemblies.
The hexagonal head allows the plug to be driven and removed with a standard open-end or box wrench on clean flat surfaces — no marring, no tooth bite marks, no body distortion. This is particularly important when plugs are installed in close-coupled manifold assemblies where adjacent fittings leave little clearance for pipe wrench jaws. The hex geometry also allows torque to be applied and measured accurately, supporting documented installation procedures for critical service ports.
Standard SS 316 construction resists chloride environments, sour gas (H2S), process chemicals, steam condensate, and offshore atmospheric corrosion. SS 316 plugs do not corrode-seize in SS 316 manifold ports — maintenance removal after years of service remains feasible without drilling or Helicoil repair. Passivated surface finish minimises thread galling risk during installation and removal.
From 1/16" miniature instrument vent ports to 2" main process pipe drain connections, TES-LOK hex plugs cover the complete instrument and process piping size range under one quality system. Procurement for a multi-size project can be consolidated with a single MTC batch rather than sourcing small plugs and large plugs from different suppliers with different certification trails.
Unlike single-use gaskets or self-sealing plugs, hex plugs can be removed, inspected, re-sealed with fresh PTFE tape (NPT/BSPT) or a new Dowty bonded seal (BSPP), and reinstalled multiple times. This makes them practical for test-port plugs that are accessed during commissioning, PSV set-point tests, and periodic maintenance — the plug itself is not consumed each time the port is accessed, only the sealant is replaced.
EN 10204 3.1 material test certificates are available for all SS 316 and exotic alloy hex plugs. PMI (positive material identification) testing available on request. Full heat and lot traceability supports documentation requirements for oil & gas, offshore, pharmaceutical, and nuclear instrument piping systems where every component in a pressure boundary must be certified.
▶ What is a hex plug tube fitting?
A hex plug is a solid male-threaded fitting with a hexagonal head used to seal and blank open female-threaded ports. The solid body contains no bore — it completely closes the port, preventing any fluid flow. The hex head provides wrench flats for installation and removal with an open-end wrench. Used to blank spare manifold ports, cap test connections, seal vent/drain points, and close dead-end ports on valves, instruments, and piping assemblies.
▶ What is the difference between a hex plug and a hex cap?
A hex plug has a male external thread — it screws into a female-threaded port. A hex cap has a female internal thread — it screws onto a male-threaded nipple or stud. Both completely seal their respective connections. Use a hex plug when the port to be sealed is a female socket; use a hex cap when the component to be capped is a male stud or nipple.
▶ What sealant do I need for a BSPP hex plug?
A Dowty bonded seal (bonded washer) fitted on the BSPP plug shoulder — not PTFE tape. BSPP is a parallel thread and does not seal by taper engagement. The Dowty seal compresses between the plug shoulder and the port entry face to create the seal. PTFE tape on BSPP creates a false torque feel without sealing and will leak.
▶ Can a hex plug be reused after removal?
Yes — typically 3–5 times on NPT/BSPT, provided the thread is inspected and found undamaged. Apply fresh PTFE tape each re-installation. For BSPP, fit a new Dowty bonded seal each time — do not re-use the compressed washer. Inspect threads for galling, corrosion, or cross-thread damage before deciding on re-use. Replace if in doubt.
▶ Are NPT and BSPT hex plugs interchangeable?
No. NPT (60° flank angle) and BSPT (55° flank angle) have different thread pitches and included angles — they are not interchangeable. Threading an NPT plug into a BSPT port (or vice versa) causes cross-threading that appears to engage but will leak or fail under pressure. Always match plug thread standard to port thread standard.
▶ What sizes are available?
1/16" to 2" in NPT, BSPT, and BSPP — all standard instrument and process pipe sizes are available from stock. Non-standard sizes manufactured on request.
▶ What materials are available?
SS 316 (standard), SS 316L, SS 304, Brass, Monel 400, Inconel 600, and Hastelloy C-276. Always match plug material to the port body material to avoid galvanic corrosion at the thread interface in wet service. EN 10204 3.1 MTCs and PMI available on request.
▶ What is the pressure rating of a hex plug?
Up to 6,000 PSI in SS 316 at ambient temperature. Brass: up to 3,000 PSI. The solid body of a hex plug is inherently stronger than a hollow fitting of the same thread size — the pressure rating is governed by thread engagement depth in the female port. Verify that the female port provides adequate thread engagement length for the plug thread size and pressure class.
SS 316 · Brass · Monel · Inconel · NPT · BSPT · BSPP · 1/16"–2" · Solid Body · ISO 9001:2015 · EN 10204 3.1 MTCs available
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