Adapting the INF-2 for Use with Different Air Coupler Standards

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Overview

The INF-2 Shop Inflator is set up from the factory with a 1/4 quick-disconnect coupler, sometimes called “M-Style”. This is the most common air hose coupler type in the United States. The coupler plug interface on the INF-2 features 3/8 NPT threading, a size which conforms to the American National Standard Pipe Thread standard. A 3/8 NPT thread has 18 TPI and a nominal OD (outside diameter) of 0.675″ (17.1 mm).

The above details are important when changing the coupler plug configuration of the INF-2. Countries outside the United States may use any number of other coupler plug standards. Featured in this article are a selection of other couplers that you may run into, along with their threading information.

Style

The style of coupler refers to the shape and design of the coupler. The shape and style influence compatibility and flow rate.

Flow Size

The flow size, also referred to as coupler size, is a reference to the size of the coupler. Despite what the name may indicate, this does not refer to the inner diameter (where the air flows) but the outer diameter and length of the coupler tip. Different coupler styles are often available in different flow sizes.

Threading

Coupler plugs are typically installed into air tools using threads. These are commonly threads that follow American National Standard Pipe Thread or British Standard Pipe (BSP) conventions.

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Coupler Styles

Most coupler styles can be identified or narrowed down by comparing them to example pictures. Identifying flow size is the best done by measuring the plug tip outer diameter (A in the example pictures) and plug tip length (B in the example pictures).

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Industrial Quick-Disconnect

Industrial couplers are very common in the USA. There are different sizes of coupler under this system. Milton is a commonly-used brand that has their own naming convention for these in its different sizes. The most common flow size is 1/4 — in Milton’s lineup this is referred to as “M-Style”. 3/8 flow size is referred to as “H-Style”. 1/2 flow size is referred to as “G-Style”. Milton does not make industrial couplers in 1/8 or 3/4 sizes, but other coupler manufacturers do.

Flow Size	Plug Tip Diameter (A)	Plug Tip Length (B)
1/8	1/4″ (6.35 mm)	1/8″ (3.18 mm)
1/4	5/16″ (7.94 mm)	3/16″ (4.76 mm)
3/8	7/16″ (11.11 mm)	5/16″ (7.94 mm)
1/2	9/16″ (14.29 mm)	3/8″ (9.5 mm)
3/4	13/16″ (20.64 mm)	5/16″ (7.94 mm)

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Tru-Flate®

Tru-Flate® couplers, also referred to as automotive couplers, come in 3 flow sizes.

Flow Size	Plug Tip Diameter (A)	Plug Tip Length (B)
1/4	3/8” (9.52 mm)	1/16” (1.59 mm)
3/8	7/16” (11.11 mm)	1/8” (3.18 mm)
1/2	9/16” (14.29 mm)	1/8” (3.18 mm)

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ARO

ARO couplers, also known as Milton A-Style, come in two flow sizes: 1/4 and 3/8. They are available in 1/4 NPT, 3/8 NPT, and BSPT threading.

Flow Size	Plug Tip Diameter (A)	Plug Tip Length (B)
1/4 (NPT)	5/16 (7.94 mm)	5/16 (7.94 mm)
1/4 (BSPT)	5/16 (7.94 mm)	3/8” (9.52 mm)
3/8(NPT)	7/16” (11.11 mm)	9/16” (14.29 mm)

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European Quick-Disconnect

European Quick-Disconnect fittings (also known as Milton V-Style, Coilhose Megaflow, NT 7.2, or DIN 7.2) are only available in one flow size but many different thread sizes. They are also the most common coupler style in Europe and are sometimes called “workshop couplers” in Germany and other countries.

Flow Size	Plug Tip Diameter (A)	Plug Tip Length (B)
1/4	3/8” (9.52 mm)	3/16 (4.76 mm)

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Japanese Quick-Disconnect

Japanese Quick disconnect fittings are only available in one flow size but many different thread sizes.

Flow Size	Plug Tip Diameter (A)	Plug Tip Length (B)
1/4	7/16” (11.11 mm)	7/32” (5.56 mm)

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Silverline Bayonet Couplers

These couplers are commonly found in the UK.

Flow Size	Plug Tip Diameter (A)	Plug Tip Length (B)
3/16	5/16″ (7.91mm)	11/32″ (8.72mm)

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Lincoln

There is only one size of coupler for Lincoln fittings. All Lincoln fittings work with all Lincoln couplers.

Flow Size	Plug Tip Diameter (A)	Plug Tip Length (B)
1/4	9/32” (7.14 mm)	3/4” (19.05 mm)

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Schrader Quick-Connect

Also known as the Twist Lock.

Flow Size	Plug Tip Diameter (A)	Plug Tip Length (B)
1/4	5/16″ (7.94 mm)	3/4″ (19.05 mm)
1/2	1/2″ (12.70 mm)	7/8″ (22.22 mm)

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Threading

As noted above, coupler plugs are typically installed into air tools using threads. There are a few thread sizes and standards that are more common in the world of air tools.

The INF-2 uses 3/8 NPT threading (an American National Standard Pipe Thread standard) to secure the plug. NPT is a common thread standard in the USA and Canada for connections that need to seal. The thread is tapered and wedges together when tightened to create a seal. It is suggested that you use a sealing tape or sealant when fitting these together.

BSPT thread (a British Standard Pipe standard) is similar to NPT but has a different thread angle and in many cases a different thread pitch. This is commonly found in the UK, China and Japan but is rarely seen in the USA or Canada.

BSPP thread (another British Standard Pipe standard) is not tapered like NPT or BSPT. It uses a seal at the shoulder of the male fitting and face of the female fitting. The seal is typically copper.

Adapters

If you cannot source a coupler plug with your choice of coupler style and 3/8 NPT threading, there are adapters available to adapt other thread standards to 3/8 NPT.

The above adapter example features 3/8 BSPP female threading and 3/8 NPT male threading, allowing the installation of a coupler plug with 3/8 BSPP threading to be installed into the INF-2.