A hex head plug is a pipe fitting with an external hex head. It seals the end of a threaded pipe, port, or opening—either permanently or just for temporary use. You tighten or loosen it with a standard wrench or socket. This article shows you how to read hex head plug dimensions and gives you complete size charts for NPT, ISO tapered, ISO parallel, and metric threads.
How to Read Hex Head Plug Dimensions
Hex head pipe plug dimensions depend on whether you use inch or metric standards. Hex head plug dimension tables typically include three key measurements:
| Symbol | Name | What it means |
| L | Panjang | Total length of the plug. Measure from the top of the hex head to the end of the threads. |
| F | Hex / Wrench Size | Width across the flats of the hex head. This is the wrench or socket size you need. |
| B | Thread Length | How much of the plug is threaded. This is the part that screws into the female threads. |
NPT Hex Head Plug Dimensions
NPT is the go-to thread in North America. It follows ASME B1.20.1. The table below covers NPTLOK hex head plugs from 1/16″ to 1 1/2″. Inches first, millimeters in parentheses.
NPT threads are self-sealing due to their tapered design. When tightening an NPT hex head plug, the threads deform slightly to fill gaps and create a metal-to-metal seal. For additional sealing security, PTFE tape or thread sealant is commonly applied.
ISO Tapered Thread
ISO tapered threads—also called BSPT or R threads—are common in Europe and many other regions. They follow ISO 7/1 and BS EN 10226-1. The table below gives hex head plug dimensions for these threads, from 1/16″ to 2″.
ISO tapered threads have a 1:16 taper and a 55° thread angle, which differs from the 60° angle of NPT threads. They are not interchangeable with NPT threads, although they have similar nominal sizes. Attempting to join an NPT male to a BSPT female will cause the joint to get stuck within a few turns. But you can connect them through adapters.
ISO Parallel Thread
ISO parallel threads (also known as BSPP or G threads) are straight threads governed by ISO 228. They require a sealing washer or O-ring to achieve a leak-free seal because the threads themselves do not provide a sealing action. The table below shows hex head plug dimensions for ISO parallel threads from 1/8″ to 1″.
ISO parallel threads are commonly found in hydraulic and pneumatic systems, as well as in European instrumentation applications. Always use a bonded washer or O-ring with BSPP plugs to ensure a proper seal.
Metric Thread
Metric threads (M threads) are specified by nominal diameter and pitch, such as M14 x 1.5. They are governed by ISO 261 and ISO 262. The table below shows hex head plug dimensions for metric threads from M14 x 1.5 to M27 x 2.
Metric hex head plugs are used in a wide range of industrial equipment, particularly in European machinery and automotive applications. The M series threads conform to ISO 261 (general purpose metric screw threads) and ISO 262 (selected sizes for screws, bolts, and nuts).
How to Choose the Right Hex Head Plug
Picking a hex head plug isn’t complicated, but you do need to get four things right: thread type, size, material, and pressure rating.
Thread type is the big one. Get this wrong and nothing else matters. NPT is what you’ll find in North America. In Europe, it’s mostly ISO tapered (R) or ISO parallel (G). Metric (M) threads show up in European machinery and automotive stuff. Just don’t mix them. An NPT plug in a BSPT port won’t seal. Even if the sizes look close.
Size is next. Match it to your pipe or port. The tables in this article give you L, F, and B. The F dimension—that’s your wrench size. Don’t overlook it.
As for material, you’ve got options. SS316, SS304, carbon steel, brass. SS316 handles corrosion well—think chemical plants, marine, nasty environments. Carbon steel is for high strength, hydraulic, heavy-duty. Brass is fine for water, oil, gas in plumbing and heating.
About Pressure rating. Plugs come in 2000 lb, 3000 lb, and 6000 lb classes. 3000 lb is the workhorse for industrial piping. 6000 lb is for extreme high pressure and hydraulics. Always check the rating for your size and application. For example, NPTLOK 1/2″ NPT in SS316 or carbon steel, Good up to 7700 psig (530 bar).
Pertanyaan yang Sering Diajukan (FAQ)
Q1. What is the difference between hex head and hollow hex plug?
A hex head plug has an external hex head, tightened with a standard wrench or socket. A hollow hex plug has an internal hex socket, tightened with an Allen key. Hex head plugs suit higher torque and external access; hollow hex plugs fit tight spaces.
Q2. Can hex head plugs be reused?
Yes, if threads are undamaged and the plug wasn’t over-tightened. Inspect threads and hex head before reuse. For critical sealing applications, replace the plug to ensure a reliable seal.
Q3. What is the maximum pressure rating for hex head plugs?
Hex head plugs come in 2000 lb, 3000 lb, and 6000 lb classes. Actual working pressure depends on size, material, and thread. Example: NPTLOK 1/2-inch NPT SS316 plugs handle up to 7700 psig (530 bar).
Q4. What is the wrench size for a 1/2″ NPT hex head plug?
For NPTLOK 1/2-inch NPT hex head plugs (SS-TPP-MN8), the F (Hex) dimension is 0.87 inch (22.2 mm). Use a 7/8-inch wrench or socket.
Choose reliable hex head plugs supplier
NPTLOK is a manufacturer of hex head plugs and other precision pipe fittings, with over 20 years of production experience and ISO 9001:2015 certification. We supply SS316, SS304, carbon steel, and brass hex head plugs in NPT, ISO tapered, ISO parallel, and metric threads.
For custom sizes, OEM orders, or technical inquiries, please Hubungi kami. We offer MOQ from 10 pcs for trial orders and can provide material certificates and test reports upon request.
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