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Foster 4 Series Couplers

The Foster 4 Series is the 3/8" body industrial interchange, one of the most common air coupler sizes for shop and industrial use. This collection includes 4 Series couplers and plugs in brass, steel, and stainless with NPT, hose barb, push-on, and reusable terminations. Filter by thread, material, and coupler or plug to match your line.

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$ 5.39
$ 5.39 - $ 5.39
$ 5.39
$ 4.29
$ 4.29 - $ 4.29
$ 4.29

Foster 40-4, 4 Series, Industrial Plug, 1/4" Male NPT, Steel

Reliable, leak-free 3/8" connections for air and fluid lines. The Foster 40-4 is a Steel 3/8" industrial plug from the Foster 4 Series — a high-flo...

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$ 5.39
$ 5.39 - $ 5.39
$ 5.39
$ 4.29
$ 4.29 - $ 4.29
$ 4.29
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$ 31.99
$ 31.99 - $ 31.99
$ 31.99
$ 25.59
$ 25.59 - $ 25.59
$ 25.59

Foster FM4204, 4 Series, Industrial Coupler, Automatic, 3/8" Female NPT, Brass

Reliable, leak-free 3/8" connections for air and fluid lines. The Foster FM4204 is a Brass 3/8" industrial coupler from the Foster 4 Series — a hig...

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$ 31.99
$ 31.99 - $ 31.99
$ 31.99
$ 25.59
$ 25.59 - $ 25.59
$ 25.59
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$ 6.69
$ 6.69 - $ 6.69
$ 6.69
$ 5.39
$ 5.39 - $ 5.39
$ 5.39

Foster 43-4, 4 Series, Industrial Plug, 3/8" Female NPT, Steel

Reliable, leak-free 3/8" connections for air and fluid lines. The Foster 43-4 is a Steel 3/8" industrial plug from the Foster 4 Series — a high-flo...

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$ 6.69
$ 6.69 - $ 6.69
$ 6.69
$ 5.39
$ 5.39 - $ 5.39
$ 5.39
Save 19% Save %
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$ 31.99
$ 31.99 - $ 31.99
$ 31.99
$ 25.59
$ 25.59 - $ 25.59
$ 25.59

Foster FM4303, 4 Series, Industrial Coupler, Automatic, 3/8" Male NPT, Brass

Reliable, leak-free 3/8" connections for air and fluid lines. The Foster FM4304 is a Brass 3/8" industrial coupler from the Foster 4 Series — a hig...

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$ 31.99
$ 31.99 - $ 31.99
$ 31.99
$ 25.59
$ 25.59 - $ 25.59
$ 25.59
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$ 8.99
$ 8.99 - $ 8.99
$ 8.99
$ 7.19
$ 7.19 - $ 7.19
$ 7.19

Foster 42-4B, 4 Series, Industrial Plug, 3/8" Male NPT, Brass

Reliable, leak-free 3/8" connections for air and fluid lines. The Foster 42-4B is a Brass 3/8" industrial plug from the Foster 4 Series — a high-fl...

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$ 8.99
$ 8.99 - $ 8.99
$ 8.99
$ 7.19
$ 7.19 - $ 7.19
$ 7.19
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$ 5.39
$ 5.39 - $ 5.39
$ 5.39
$ 4.29
$ 4.29 - $ 4.29
$ 4.29

Foster 41-4, 4 Series, Industrial Plug, 1/4" Female NPT, Steel

Reliable, leak-free 3/8" connections for air and fluid lines. The Foster 41-4 is a Steel 3/8" industrial plug from the Foster 4 Series — a high-flo...

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$ 5.39
$ 5.39 - $ 5.39
$ 5.39
$ 4.29
$ 4.29 - $ 4.29
$ 4.29
Save 20% Save %
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$ 31.99
$ 31.99 - $ 31.99
$ 31.99
$ 25.59
$ 25.59 - $ 25.59
$ 25.59

Foster FM4304, 4 Series, Industrial Coupler, Automatic, 3/8" Male NPT, Brass

Reliable, leak-free 3/8" connections for air and fluid lines. The Foster FM4304 is a Brass 3/8" industrial coupler from the Foster 4 Series — a hig...

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$ 31.99
$ 31.99 - $ 31.99
$ 31.99
$ 25.59
$ 25.59 - $ 25.59
$ 25.59
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$ 23.39
$ 23.39 - $ 23.39
$ 23.39
$ 18.79
$ 18.79 - $ 18.79
$ 18.79

Foster 4004, 4 Series, Industrial Coupler, Manual, 1/4" Female NPT, Brass, Steel

Reliable, leak-free 3/8" connections for air and fluid lines. The Foster 4004 is a Brass/Steel 3/8" industrial coupler from the Foster 4 Series — a...

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$ 23.39
$ 23.39 - $ 23.39
$ 23.39
$ 18.79
$ 18.79 - $ 18.79
$ 18.79
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$ 31.79
$ 31.79 - $ 31.79
$ 31.79
$ 25.39
$ 25.39 - $ 25.39
$ 25.39

Foster FM4004, 4 Series, Industrial Coupler, Automatic, 1/4" Female NPT, Brass

Reliable, leak-free 3/8" connections for air and fluid lines. The Foster FM4004 is a Brass 3/8" industrial coupler from the Foster 4 Series — a hig...

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$ 31.79
$ 31.79 - $ 31.79
$ 31.79
$ 25.39
$ 25.39 - $ 25.39
$ 25.39
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$ 24.19
$ 24.19 - $ 24.19
$ 24.19
$ 19.39
$ 19.39 - $ 19.39
$ 19.39

Foster 4204, 4 Series, Industrial Coupler, Manual, 3/8" Female NPT, Brass, Steel

Reliable, leak-free 3/8" connections for air and fluid lines. The Foster 4204 is a Brass/Steel 3/8" industrial coupler from the Foster 4 Series — a...

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$ 24.19
$ 24.19 - $ 24.19
$ 24.19
$ 19.39
$ 19.39 - $ 19.39
$ 19.39
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$ 32.79
$ 32.79 - $ 32.79
$ 32.79
$ 26.19
$ 26.19 - $ 26.19
$ 26.19

Foster FM4404, 4 Series, Industrial Coupler, Automatic, 1/2" Female NPT, Brass

Reliable, leak-free 3/8" connections for air and fluid lines. The Foster FM4404 is a Brass 3/8" industrial coupler from the Foster 4 Series — a hig...

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$ 32.79
$ 32.79 - $ 32.79
$ 32.79
$ 26.19
$ 26.19 - $ 26.19
$ 26.19
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$ 6.99
$ 6.99 - $ 6.99
$ 6.99
$ 5.59
$ 5.59 - $ 5.59
$ 5.59

Foster 44-4, 4 Series, Industrial Plug, 1/2" Male NPT, Steel

Reliable, leak-free 3/8" connections for air and fluid lines. The Foster 44-4 is a Steel 3/8" industrial plug from the Foster 4 Series — a high-flo...

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$ 6.99
$ 6.99 - $ 6.99
$ 6.99
$ 5.59
$ 5.59 - $ 5.59
$ 5.59
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$ 9.29
$ 9.29 - $ 9.29
$ 9.29
$ 7.39
$ 7.39 - $ 7.39
$ 7.39

Foster 45-4, 4 Series, Industrial Plug, 1/2" Female NPT, Steel

Reliable, leak-free 3/8" connections for air and fluid lines. The Foster 45-4 is a Steel 3/8" industrial plug from the Foster 4 Series — a high-flo...

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$ 9.29
$ 9.29 - $ 9.29
$ 9.29
$ 7.39
$ 7.39 - $ 7.39
$ 7.39
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$ 32.79
$ 32.79 - $ 32.79
$ 32.79
$ 26.19
$ 26.19 - $ 26.19
$ 26.19

Foster FM4804, 4 Series, Industrial Coupler, Automatic, 3/8" Hose Barb, Brass

Reliable, leak-free 3/8" connections for air and fluid lines. The Foster FM4804 is a Brass 3/8" industrial coupler from the Foster 4 Series — a hig...

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$ 32.79
$ 32.79 - $ 32.79
$ 32.79
$ 26.19
$ 26.19 - $ 26.19
$ 26.19
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$ 9.89
$ 9.89 - $ 9.89
$ 9.89
$ 7.99
$ 7.99 - $ 7.99
$ 7.99

Foster 48-4B, 4 Series, Industrial Plug, 3/8" Hose Barb, Brass

Reliable, leak-free 3/8" connections for air and fluid lines. The Foster 48-4B is a Brass 3/8" industrial plug from the Foster 4 Series — a high-fl...

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$ 9.89
$ 9.89 - $ 9.89
$ 9.89
$ 7.99
$ 7.99 - $ 7.99
$ 7.99
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$ 24.09
$ 24.09 - $ 24.09
$ 24.09
$ 19.29
$ 19.29 - $ 19.29
$ 19.29

Foster 4104, 4 Series, Industrial Coupler, Manual, 1/4" Male NPT, Brass, Steel

Reliable, leak-free 3/8" connections for air and fluid lines. The Foster 4104 is a Brass/Steel 3/8" industrial coupler from the Foster 4 Series — a...

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$ 24.09
$ 24.09 - $ 24.09
$ 24.09
$ 19.29
$ 19.29 - $ 19.29
$ 19.29
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$ 31.79
$ 31.79 - $ 31.79
$ 31.79
$ 25.39
$ 25.39 - $ 25.39
$ 25.39

Foster FM4104, 4 Series, Industrial Coupler, Automatic, 1/4" Male NPT, Brass

Reliable, leak-free 3/8" connections for air and fluid lines. The Foster FM4104 is a Brass 3/8" industrial coupler from the Foster 4 Series — a hig...

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$ 31.79
$ 31.79 - $ 31.79
$ 31.79
$ 25.39
$ 25.39 - $ 25.39
$ 25.39
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$ 34.79
$ 34.79 - $ 34.79
$ 34.79
$ 27.89
$ 27.89 - $ 27.89
$ 27.89

Foster FM1714, 4 Series, Industrial Coupler, Automatic, 3/8" Push-On Hose Barb, Brass

Reliable, leak-free 3/8" connections for air and fluid lines. The Foster FM1714 is a Brass 3/8" industrial coupler from the Foster 4 Series — a hig...

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$ 34.79
$ 34.79 - $ 34.79
$ 34.79
$ 27.89
$ 27.89 - $ 27.89
$ 27.89
Save 20% Save %
Save 21% Save %
$ 9.19
$ 9.19 - $ 9.19
$ 9.19
$ 7.29
$ 7.29 - $ 7.29
$ 7.29

Foster 40-4B, 4 Series, Industrial Plug, 1/4" Male NPT, Brass

Reliable, leak-free 3/8" connections for air and fluid lines. The Foster 40-4B is a Brass 3/8" industrial plug from the Foster 4 Series — a high-fl...

View full details
$ 9.19
$ 9.19 - $ 9.19
$ 9.19
$ 7.29
$ 7.29 - $ 7.29
$ 7.29
Save 21% Save %
Save 20% Save %
$ 32.39
$ 32.39 - $ 32.39
$ 32.39
$ 25.89
$ 25.89 - $ 25.89
$ 25.89

Foster FM4504, 4 Series, Industrial Coupler, Automatic, 1/2" Male NPT, Brass

Reliable, leak-free 3/8" connections for air and fluid lines. The Foster FM4504 is a Brass 3/8" industrial coupler from the Foster 4 Series — a hig...

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$ 32.39
$ 32.39 - $ 32.39
$ 32.39
$ 25.89
$ 25.89 - $ 25.89
$ 25.89
Save 20% Save %
Save 20% Save %
$ 27.99
$ 27.99 - $ 27.99
$ 27.99
$ 22.39
$ 22.39 - $ 22.39
$ 22.39

Foster 4404, 4 Series, Industrial Coupler, Manual, 1/2" Female NPT, Brass, Steel

Reliable, leak-free 3/8" connections for air and fluid lines. The Foster 4404 is a Brass/Steel 3/8" industrial coupler from the Foster 4 Series — a...

View full details
$ 27.99
$ 27.99 - $ 27.99
$ 27.99
$ 22.39
$ 22.39 - $ 22.39
$ 22.39
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Save 20% Save %
$ 27.99
$ 27.99 - $ 27.99
$ 27.99
$ 22.39
$ 22.39 - $ 22.39
$ 22.39

Foster 4504, 4 Series, Industrial Coupler, Manual, 1/2" Male NPT, Brass, Steel

Reliable, leak-free 3/8" connections for air and fluid lines. The Foster 4504 is a Brass/Steel 3/8" industrial coupler from the Foster 4 Series — a...

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$ 27.99
$ 27.99 - $ 27.99
$ 27.99
$ 22.39
$ 22.39 - $ 22.39
$ 22.39
Save 20% Save %
Save 21% Save %
$ 6.29
$ 6.29 - $ 6.29
$ 6.29
$ 4.99
$ 4.99 - $ 4.99
$ 4.99

Foster 48-4, 4 Series, Industrial Plug, 3/8" Hose Barb, Steel

Reliable, leak-free 3/8" connections for air and fluid lines. The Foster 48-4 is a Steel 3/8" industrial plug from the Foster 4 Series — a high-flo...

View full details
$ 6.29
$ 6.29 - $ 6.29
$ 6.29
$ 4.99
$ 4.99 - $ 4.99
$ 4.99
Save 21% Save %
Save 20% Save %
$ 33.19
$ 33.19 - $ 33.19
$ 33.19
$ 26.59
$ 26.59 - $ 26.59
$ 26.59

Foster FM4904, 4 Series, Industrial Coupler, Automatic, 1/2" Hose Barb, Brass

Reliable, leak-free 3/8" connections for air and fluid lines. The Foster FM4904 is a Brass 3/8" industrial coupler from the Foster 4 Series — a hig...

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$ 33.19
$ 33.19 - $ 33.19
$ 33.19
$ 26.59
$ 26.59 - $ 26.59
$ 26.59
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