Plugs, Adapters, & Vents

How to Pick the Right Drum Plug.

Selecting the correct drum plug, thread type, and closure configuration is critical for safety, compliance, and product integrity. Below are answers to common questions regarding drum bungs, plugs, flanges, threads, compatibility, and UN/DOT considerations.

What is a flange?

The flange is the female-threaded fitting in the top or cover that accepts the plug.

• A round head plug fits an octagonal base flange.
• A hex head plug fits a circular base flange.

What drum plug do I need?

To determine the correct plug, confirm:

1. Drum material: Plastic or steel
2. Bung size: 2" or ¾" (most common sizes)
3. Thread type: Buttress, NPS, or NPT
4. Flange type: Octagonal (round-head plug) or circular (hex-head plug)

Round-head plugs are used on drums with a raised octagonal flange.
Hex-head plugs are used on drums with a flat circular flange.

What is the difference between Round Head and Hex Head steel plugs?

Round Head Steel Plugs
Have a very thin gasket and a stamped metal clip welded into the center for the wrench to go.

Hex Head Steel Plugs
Have a six-sided shape and often a center, heavy stamped bar welded in the center for the wrench.

What thread types am I working with?

NPS (National Pipe Straight)

• Straight threads
• Used in steel drum plugs
• Requires a gasket to create a seal

NPT (National Pipe Tapered)

• 11-1/2 threads per inch in 2" size
• Tapered male threads (commonly on faucets)
• Seals as threads tighten and “jam”
• Pipe sealing tape is recommended, especially for thin liquids

Buttress Threads

• Coarse, sawtooth-shaped thread design
• Common on polyethylene drum plugs
• Thicker and spaced farther apart
• Designed for easier molding in plastic drums

Most plastic drums still include a 2" buttress-threaded bung. The plug may include a ¾" NPS center to accommodate a faucet.

Why do plastic drums have two different 2 inch bung openings?

All plastic plugs have a round shape, regardless of the bung opening they're intended to fit, but threading can be different.

1. A 2" NPS opening that takes something like a PPA57GK plug or a G2CPP plug
2. An opening with some very heavy coarse, thread in it known as the "buttress" thread: Doesn't fit any standard faucets or pumps. Buttress threads are a holdover from the early days of plastic drums. Back then, it was difficult to precisely mold pipe threads directly into the drum. NPS plugs would leak, cross thread, or strip out when you tightened them. The heavy, strong buttress thread solved the problem. Today, plastic drum technology is vastly improved, and NPS plugs now perform just as well as buttress plugs.

What is a buttress adapter?

A buttress adapter converts buttress threads on a plastic drum to 2" NPT threads.

This allows you to install:

• 2" faucets
• Pumps
• Funnels

There are three or four different types of buttress drum threads, depending on who made your drum. We have adapters (whether for your 8 gallon drums, 10 gallon drums, and onward) to convert almost any buttress opening to accept an NPS-threaded accessory.

Does a steel drum need to be recertified for UN/DOT Compliance when steel plugs are replaced with fusible plugs?

Yes, replacing standard steel plugs with fusible plugs is considered a change in closure. This requires recertification and testing requirements apply when closures are modified. 

What is the difference between pressure or vacuum relief in a drum plug?

Vacuum relief plugs (vent-in) allow air to enter the container while the contents is pumped or drained out, preventing the container from collapsing due to vacuum. Pressure relief plugs (vent-out) prevent the buildup of pressure inside the drum during storage. Drums containing flammable liquids require an approved flash-arresting vent-out plug.

If you need help identifying the correct plug, thread type, or closure configuration, contact our BASCO Customer Service Experts. We Contain It All.

How to Pick the Right Drum Plug.

Round-Head Steel Plugs: Have a very thin gasket and a stamped metal clip welded into the center for the wrench to go

Hex-head Steel Plugs: Have a six-sided shape and often a center, heavy stamped bar welded in the center for the wrench

Ready for some confusion? All plastic plugs have a round shape, regardless of the bung opening they're intended to fit.

So look at the bung opening in your steel drum.

Base has eight sides? Takes a round-head type plug

Mostly round, but has many little points around it? Takes a hex-head type plug

Plastic drums usually have two openings:

1. A 2" NPS opening that takes something like a PPA57GK plug or a G2CPP plug
2. An opening with some very heavy coarse, weird thread in it known as the dreaded "buttress" thread: Doesn't fit any standard faucets or pumps. Buttress threads are a holdover from the early days of plastic drums. Back then, it was difficult to precisely mold pipe threads directly into the drum. NPS plugs would leak, cross thread, or strip out when you tightened them. The heavy, strong buttress thread solved the problem. Today, plastic drum technology is vastly improved, and NPS plugs now perform just as well as buttress plugs.

There are three or four different types of buttress drum threads, depending on who made your drum. We have adapters (whether for your 8 gallon drums, 10 gallon drums, and onward) to convert almost any buttress opening to accept an NPS-threaded accessory.