Header & Shoulder Plugs & Gaskets
API 661 type hex head UNF plugs for header boxes on air-cooled heat exchangers and fin-fan coolers. CNC-machined, marked to the heat number, and supplied as matched plug & gasket sets.
ALSO KNOWN AS: HEX HEAD PLUGS · UNF PLUGS · FIN-FAN PLUGS · HEAT EXCHANGER PLUG & GASKET SETS
Direct access to every tube. A leak-tight seal when you close up.
Metalok header plugs thread into the plug sheet of air-cooled heat exchanger header boxes, giving maintenance teams direct access to every tube for inspection, cleaning and tube plugging. They then seal back leak-tight against process pressure and temperature.
Widely used across upstream production, refineries, petrochemical plants and power facilities, spare plug & gasket sets are essential stock for every turnaround.
- CNC-machined shoulder plug: precision UNF thread, 63 RMS gasket seating face
- High-volume production capacity per day, with fast delivery from stock
- 100% traceability: marked with material & heat number
Enter your tube size. Get the exact plug, gasket and torque.
Built from Metalok's own sizing chart. The drawing redraws to scale as you choose, and the full specification is ready to add to your RFQ.
Configure your plug
Plugs, gaskets & recommended minimum torque.
| Base dimensions (API 661 type) | Flat gasket | ||||||
|---|---|---|---|---|---|---|---|
| Typical tube O.D. | "A" plug diameter | Typical UNF (TPI) | "B" length under head** | Hex size | Stock # | Min. torque (ft-lbs)* | RFQ |
| 5/8 in | 3/4 in | 16 | 3/4" – 3" | 1 in | MISP-G-0750-<> | 200 | |
| 3/4 in | 7/8 in | 14 | 3/4" – 3" | 1-1/8 in | MISP-G-0875-<> | 265 | |
| 7/8 in | 1 in | 12 | 3/4" – 3" | 1-1/4 in | MISP-G-1000-<> | 300 | |
| 1 in | 1-1/8 in | 12 | 3/4" – 3" | 1-3/8 in | MISP-G-1125-<> | 395 | |
| 1-1/8 in | 1-1/4 in | 12 | 3/4" – 3" | 1-1/2 in | MISP-G-1250-<> | 490 | |
| 1-1/4 in | 1-3/8 in | 12 | 3/4" – 3" | 1-5/8 in | MISP-G-1375-<> | 580 | |
| 1-3/8 in | 1-1/2 in | 12 | 3/4" – 3" | 1-3/4 in | MISP-G-1500-<> | 690 | |
| 1-1/2 in | 1-5/8 in | 12 | 3/4" – 3" | 1-7/8 in | MISP-G-1625-<> | 800 | |
| 1-5/8 in | 1-3/4 in | 12 | 3/4" – 3" | 2 in | MISP-G-1750-<> | 900 | |
| 1-3/4 in | 1-7/8 in | 12 | 3/4" – 3" | 2-1/8 in | MISP-G-1875-<> | 1000 | |
| 1-7/8 in | 2 in | 12 | 3/4" – 3" | 2-1/4 in | MISP-G-2000-<> | 1100 | |
| 2 in | 2-1/8 in | 12 | 3/4" – 3" | 2-3/8 in | MISP-G-2125-<> | 1200 | |
* Recommended minimum torque based on proper installation with carbon steel material; consult factory for other alloys. If plugs leak, increase torque in increments of 25 ft-lbs until a seal is obtained. ** Typically stocked lengths 3/4" up to 3".
Twelve alloys, one order code each.
Tap a material to load it into the plug finder. The code letter completes your gasket stock number.
Matched sets. Every length. Ready from stock.
Plugs & gaskets as matched sets
Each plug ships with its correctly sized flat gasket, so there's no sorting or mismatch on site.
Lengths 3/4" to 3"
Length under head "B" is selected to suit your header plate thickness. Non-standard lengths made to order.
Built for turnaround crews
Clean threads, crisp marking and a true sealing face: parts that go in fast and come out clean at the next shutdown.
Four details. One accurate quote.
| Plug Ø (in) | O.D. (in) | I.D. (in) | Thk. (in) |
|---|---|---|---|
| 3/4" | 1.000 | 0.750 | 0.060 |
| 7/8" | 1.125 | 0.875 | 0.060 |
| 1" | 1.250 | 1.000 | 0.060 |
| 1-1/8" | 1.375 | 1.125 | 0.060 |
| 1-3/8" | 1.625 | 1.375 | 0.060 |
| 1-5/8" | 1.875 | 1.625 | 0.060 |
| 1-7/8" | 2.125 | 1.875 | 0.060 |
| 2-1/8" | 2.375 | 2.125 | 0.060 |
Flat & low-torque (EZ-type) gaskets in soft iron, CS, 316 SS & alloy grades, matched to plug material & service. Intermediate sizes on request.
- ISO 9001:2015, CE & PED certified manufacturing
- Plugs marked: METALOK + material + heat number
- EN 10204 3.1 / 3.2 certificates with every supply
- 100% thread gauging; 63 RMS gasket seating face
- Anti-seize lubricant recommended at installation
Never stand in front of an installed plug under pressure. Plugs ejected under pressure can cause serious bodily injury. Depressurise & isolate before removing plugs.
Datasheets & documents.
Send the spec.
Get a priced quote within one working day.
Tell us the product, size, material and quantity. Attach a drawing or datasheet if you have one, and our sales engineers will come back with price, lead time and certification scope.
What buyers ask before they order.
Start from the tube O.D. in your exchanger. The plug diameter "A" and UNF thread follow from it (see the sizing chart or the Plug Finder above). Then confirm the length under head "B" to suit your header plate thickness.
Typically stocked lengths run from 3/4" up to 3". Other lengths are made to order.
Yes. Base dimensions follow the API 661 type for air-cooled heat exchanger header boxes. Custom dimensions and threads are available to your spec.
Yes. Plugs and flat gaskets are supplied as matched sets, so every plug arrives with the correct gasket OD and ID.
Carbon steel (SA-105 / SA-350 LF2), 316/304 SS, Chrome-Moly F11, Monel 400, Inconel 625/825, Titanium, Brass, 70/30 and 90/10 CuNi, Nickel 200, Hastelloy and Zirconium. Duplex/Super Duplex (F51/F53) and 904L are also available on request.
Soft iron, carbon steel and 316 SS flat gaskets are common. Low-torque (EZ-type) gaskets are also available, matched to the plug material and service.
Yes: cadmium, electroless nickel, galvanized, nickel or zinc, or supplied uncoated.
Recommended minimum torque values (ft-lbs) are given per size in the chart, based on proper installation with carbon steel material. Consult us for other alloys. If a plug leaks, increase torque in increments of 25 ft-lbs until the seal is obtained.
Yes. An anti-seize lubricant on the threads is recommended at installation to prevent galling and ease future removal.
Never. Do not stand in front of an installed plug under pressure; plugs ejected under pressure can cause serious injury. Depressurise and isolate the exchanger before removing plugs.