Header & Shoulder Plugs
Precision-machined plugs with matched flat gaskets for air-cooled heat exchanger header boxes — 12 sizes, 12 alloys, laser-marked for full traceability.
One plug per tube.
Zero excuses for a leak.
In an air-cooled exchanger every tube is reached through a threaded hole in the plug sheet. Each hole is closed by a header plug and a flat gasket. Metalok machines both — to API 661-type dimensions or to your drawing.
- Matched setsPlug and gasket supplied together, sized to each other.
- Laser-marked headsMetalok, grade, thread size and heat number.
- Gauged threadsUNF threads checked go / no-go, every piece.
- Shutdown-readyFast dispatch from stock; no minimum order.
Build your plug.
Watch it take shape.
Choose size, length, material, gasket and finish. The plug redraws to scale and the spec sheet, gasket stock number and minimum torque update live — from Metalok's own catalogue.
Tube O.D.
Select your exchanger tube O.D. — plug diameter “A” and thread follow automatically.
Length under head “B”
Match B to your plug-sheet thickness. Non-standard lengths are made to order.
Material
The material code “M” is stamped on the head and carried into the gasket stock number.
Gasket
Flat gaskets are supplied as a matched set with every plug.
Finish / coating
Supplied uncoated, or with one of five protective coatings.
Every size, one table.
From the Metalok Header Plugs catalogue (Aug 2026). Minimum torque for carbon steel with proper installation.
| Tube O.D. | Plug Ø “A” | Thread | Hex A/F | Gasket stock # | Gasket OD × ID (in / mm) | Min. torque | |
|---|---|---|---|---|---|---|---|
| 5/8" | 3/4" | 16 UNF | 1" | MISP-G-0750-M | 1.000 × 0.750 | 200 ft-lb / 271 N·m | |
| 3/4" | 7/8" | 14 UNF | 1-1/8" | MISP-G-0875-M | 1.125 × 0.875 | 265 ft-lb / 359 N·m | |
| 7/8" | 1" | 12 UNF | 1-1/4" | MISP-G-1000-M | 1.250 × 1.000 | 300 ft-lb / 407 N·m | |
| 1" | 1-1/8" | 12 UNF | 1-3/8" | MISP-G-1125-M | 1.375 × 1.125 | 395 ft-lb / 536 N·m | |
| 1-1/8" | 1-1/4" | 12 UNF | 1-1/2" | MISP-G-1250-M | On request | 490 ft-lb / 664 N·m | |
| 1-1/4" | 1-3/8" | 12 UNF | 1-5/8" | MISP-G-1375-M | 1.625 × 1.375 | 580 ft-lb / 786 N·m | |
| 1-3/8" | 1-1/2" | 12 UNF | 1-3/4" | MISP-G-1500-M | On request | 690 ft-lb / 936 N·m | |
| 1-1/2" | 1-5/8" | 12 UNF | 1-7/8" | MISP-G-1625-M | 1.875 × 1.625 | 800 ft-lb / 1085 N·m | |
| 1-5/8" | 1-3/4" | 12 UNF | 2" | MISP-G-1750-M | On request | 900 ft-lb / 1220 N·m | |
| 1-3/4" | 1-7/8" | 12 UNF | 2-1/8" | MISP-G-1875-M | 2.125 × 1.875 | 1000 ft-lb / 1356 N·m | |
| 1-7/8" | 2" | 12 UNF | 2-1/4" | MISP-G-2000-M | On request | 1100 ft-lb / 1491 N·m | |
| 2" | 2-1/8" | 12 UNF | 2-3/8" | MISP-G-2125-M | 2.375 × 2.125 | 1200 ft-lb / 1627 N·m |
“M” in the stock number = material code. Gasket dimensions not listed in the catalogue are confirmed on request.
Twelve alloys.
One code letter each.
Tap a material to load it into the configurator. Need something outside the table? Duplex, Super Duplex and 904L are made on request.
See them before you specify them.
Tap to play with sound.
When ordering, specify four things.
Give us A, TPI, B and M — or just your tube O.D. and plug-sheet thickness, and we'll work out the rest.
Follows tube O.D. — e.g. 1-1/8" for a 1" tube.
UNF — 12 TPI for most sizes, 14–16 TPI for the smallest.
3/4" to 3", to suit plug-sheet thickness.
One letter from the material table, e.g. S for 316 SS.
Quality built in
- Raw material from approved mills with original certificates
- Threads gauged go / no-go on every piece
- 63 RMS gasket seating face
- EN 10204 3.1 certificates with every consignment; 3.2 on request
- Anti-seize lubricant recommended at installation
Never remove a plug from an exchanger under pressure, and do not stand in front of an installed plug while the unit is pressurised. Plugs ejected under pressure can cause serious injury. Depressurise and isolate before removal.
If a plug leaks after installation, increase torque in steps of 25 ft-lb until the seal is obtained.
Documents your QA team will ask for.
Send your plug list.
Send a size, a drawing or just a tag number. An engineer — not a call centre — answers with price, lead time and the right grade.
Unit No. 21, Nikisha Industrial Estate, Western Express Highway, Pandurang Wadi, Mira Road East, Mumbai, Maharashtra 401107, India
Header plug questions.
Sizing, materials and installation — answered from the datasheet.
Start from the tube O.D. in your exchanger. The plug diameter “A” and UNF thread follow from it — use the configurator or the sizing chart. Then confirm the length under head “B” to suit your header plate thickness.
Typically 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 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-lb) are given per size in the chart, for proper installation with carbon steel. Consult us for other alloys. If a plug leaks, increase torque in steps of 25 ft-lb until the seal is obtained.
Yes. An anti-seize lubricant on the threads prevents galling and eases 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.