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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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Foster BLH1B, 1/8" ISO-B Hydraulic Coupler x 1/8" Female NPT, ISO-B Series, Ball Lock, Brass Save 20% Save %
$ 257.00
$ 257.00 - $ 257.00
$ 257.00
$ 205.00
$ 205.00 - $ 205.00
$ 205.00

Foster PB3-4, 3/8" Industrial Plug x Reusable Hose Fitting, 1/4" ID x 1/2" OD, 4 Series, Steel

Reliable, leak-free 3/8" connections for air and fluid lines. The Foster PB3-4 is a Steel 3/8" industrial plug from the Foster 4 Series — a high-fl...

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$ 257.00
$ 257.00 - $ 257.00
$ 257.00
$ 205.00
$ 205.00 - $ 205.00
$ 205.00
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Foster BLH1B, 1/8" ISO-B Hydraulic Coupler x 1/8" Female NPT, ISO-B Series, Ball Lock, Brass Save 19% Save %
$ 186.00
$ 186.00 - $ 186.00
$ 186.00
$ 150.00
$ 150.00 - $ 150.00
$ 150.00

Foster 81-4, 3/8" Industrial Plug x 1/2" Push-On Hose Stem, 4 Series, Steel

Reliable, leak-free 3/8" connections for air and fluid lines. The Foster 81-4 is a Steel 3/8" industrial plug from the Foster 4 Series — a high-flo...

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$ 186.00
$ 186.00 - $ 186.00
$ 186.00
$ 150.00
$ 150.00 - $ 150.00
$ 150.00
Save 19% Save %
Foster BLH1B, 1/8" ISO-B Hydraulic Coupler x 1/8" Female NPT, ISO-B Series, Ball Lock, Brass Save 20% Save %
$ 464.00
$ 464.00 - $ 464.00
$ 464.00
$ 371.00
$ 371.00 - $ 371.00
$ 371.00

Foster 71-4B, 3/8" Industrial Plug x 3/8" Push-On Hose Stem, 4 Series, Brass

Reliable, leak-free 3/8" connections for air and fluid lines. The Foster 71-4B is a Brass 3/8" industrial plug from the Foster 4 Series — a high-fl...

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$ 464.00
$ 464.00 - $ 464.00
$ 464.00
$ 371.00
$ 371.00 - $ 371.00
$ 371.00
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Foster BLH1B, 1/8" ISO-B Hydraulic Coupler x 1/8" Female NPT, ISO-B Series, Ball Lock, Brass Save 21% Save %
$ 111.00
$ 111.00 - $ 111.00
$ 111.00
$ 88.00
$ 88.00 - $ 88.00
$ 88.00

Foster 71-4, 3/8" Industrial Plug x 3/8" Push-On Hose Stem, 4 Series, Steel

Reliable, leak-free 3/8" connections for air and fluid lines. The Foster 71-4 is a Steel 3/8" industrial plug from the Foster 4 Series — a high-flo...

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$ 111.00
$ 111.00 - $ 111.00
$ 111.00
$ 88.00
$ 88.00 - $ 88.00
$ 88.00
Save 21% Save %
Foster BLH1B, 1/8" ISO-B Hydraulic Coupler x 1/8" Female NPT, ISO-B Series, Ball Lock, Brass
Save 19% Save %
$ 128.00
$ 128.00 - $ 128.00
$ 128.00
$ 104.00
$ 104.00 - $ 104.00
$ 104.00

Foster 51-4, 3/8" Industrial Plug x 1/4" Push-On Hose Stem, 4 Series, Steel

Reliable, leak-free 3/8" connections for air and fluid lines. The Foster 51-4 is a Steel 3/8" industrial plug from the Foster 4 Series — a high-flo...

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$ 128.00
$ 128.00 - $ 128.00
$ 128.00
$ 104.00
$ 104.00 - $ 104.00
$ 104.00
Save 19% Save %
Foster BLH1B, 1/8" ISO-B Hydraulic Coupler x 1/8" Female NPT, ISO-B Series, Ball Lock, Brass
Save 20% Save %
$ 121.00
$ 121.00 - $ 121.00
$ 121.00
$ 97.00
$ 97.00 - $ 97.00
$ 97.00

Foster 49-4, 3/8" Industrial Plug x 1/2" Hose ID, 4 Series, Steel

Reliable, leak-free 3/8" connections for air and fluid lines. The Foster 49-4 is a Steel 3/8" industrial plug from the Foster 4 Series — a high-flo...

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$ 121.00
$ 121.00 - $ 121.00
$ 121.00
$ 97.00
$ 97.00 - $ 97.00
$ 97.00
Save 20% Save %
Foster BLH1B, 1/8" ISO-B Hydraulic Coupler x 1/8" Female NPT, ISO-B Series, Ball Lock, Brass
Save 19% Save %
$ 171.00
$ 171.00 - $ 171.00
$ 171.00
$ 138.00
$ 138.00 - $ 138.00
$ 138.00

Foster 48-4B, 3/8" Industrial Plug x 3/8" Hose ID, 4 Series, 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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$ 171.00
$ 171.00 - $ 171.00
$ 171.00
$ 138.00
$ 138.00 - $ 138.00
$ 138.00
Save 19% Save %
Foster BLH1B, 1/8" ISO-B Hydraulic Coupler x 1/8" Female NPT, ISO-B Series, Ball Lock, Brass
Save 21% Save %
$ 109.00
$ 109.00 - $ 109.00
$ 109.00
$ 86.00
$ 86.00 - $ 86.00
$ 86.00

Foster 48-4, 3/8" Industrial Plug x 3/8" Hose ID, 4 Series, 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...

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$ 109.00
$ 109.00 - $ 109.00
$ 109.00
$ 86.00
$ 86.00 - $ 86.00
$ 86.00
Save 21% Save %
Foster BLH1B, 1/8" ISO-B Hydraulic Coupler x 1/8" Female NPT, ISO-B Series, Ball Lock, Brass
Save 20% Save %
$ 179.00
$ 179.00 - $ 179.00
$ 179.00
$ 143.00
$ 143.00 - $ 143.00
$ 143.00

Foster 47-4, 3/8" Industrial Plug x 5/16" Hose ID, 4 Series, Steel

Reliable, leak-free 3/8" connections for air and fluid lines. The Foster 47-4 is a Steel 3/8" industrial plug from the Foster 4 Series — a high-flo...

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$ 179.00
$ 179.00 - $ 179.00
$ 179.00
$ 143.00
$ 143.00 - $ 143.00
$ 143.00
Save 20% Save %
Foster BLH1B, 1/8" ISO-B Hydraulic Coupler x 1/8" Female NPT, ISO-B Series, Ball Lock, Brass
Save 20% Save %
$ 152.00
$ 152.00 - $ 152.00
$ 152.00
$ 121.00
$ 121.00 - $ 121.00
$ 121.00

Foster 46-4, 3/8" Industrial Plug x 1/4" Hose ID, 4 Series, Steel

Reliable, leak-free 3/8" connections for air and fluid lines. The Foster 46-4 is a Steel 3/8" industrial plug from the Foster 4 Series — a high-flo...

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$ 152.00
$ 152.00 - $ 152.00
$ 152.00
$ 121.00
$ 121.00 - $ 121.00
$ 121.00
Save 20% Save %
Foster BLH1B, 1/8" ISO-B Hydraulic Coupler x 1/8" Female NPT, ISO-B Series, Ball Lock, Brass
Save 21% Save %
$ 297.00
$ 297.00 - $ 297.00
$ 297.00
$ 236.00
$ 236.00 - $ 236.00
$ 236.00

Foster 44S-4, 3/8" Industrial Plug x 1/2" Male NPT, 4 Series, Free Swivel, Brass/Steel

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

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$ 297.00
$ 297.00 - $ 297.00
$ 297.00
$ 236.00
$ 236.00 - $ 236.00
$ 236.00
Save 21% Save %
Foster BLH1B, 1/8" ISO-B Hydraulic Coupler x 1/8" Female NPT, ISO-B Series, Ball Lock, Brass
Save 20% Save %
$ 224.00
$ 224.00 - $ 224.00
$ 224.00
$ 179.00
$ 179.00 - $ 179.00
$ 179.00

Foster 42S-4, 3/8" Industrial Plug x 3/8" Male NPT, 4 Series, Free Swivel, Brass/Steel

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

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$ 224.00
$ 224.00 - $ 224.00
$ 224.00
$ 179.00
$ 179.00 - $ 179.00
$ 179.00
Save 20% Save %
Foster BLH1B, 1/8" ISO-B Hydraulic Coupler x 1/8" Female NPT, ISO-B Series, Ball Lock, Brass
Save 20% Save %
$ 346.00
$ 346.00 - $ 346.00
$ 346.00
$ 278.00
$ 278.00 - $ 278.00
$ 278.00

Foster 40S-4, 3/8" Industrial Plug x 1/4" Male NPT, 4 Series, Free Swivel, Brass/Steel

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

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$ 346.00
$ 346.00 - $ 346.00
$ 346.00
$ 278.00
$ 278.00 - $ 278.00
$ 278.00
Save 20% Save %
Foster BLH1B, 1/8" ISO-B Hydraulic Coupler x 1/8" Female NPT, ISO-B Series, Ball Lock, Brass
Save 20% Save %
$ 121.00
$ 121.00 - $ 121.00
$ 121.00
$ 97.00
$ 97.00 - $ 97.00
$ 97.00

Foster 44-4, 3/8" Industrial Plug x 1/2" Male NPT, 4 Series, 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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$ 121.00
$ 121.00 - $ 121.00
$ 121.00
$ 97.00
$ 97.00 - $ 97.00
$ 97.00
Save 20% Save %
Foster BLH1B, 1/8" ISO-B Hydraulic Coupler x 1/8" Female NPT, ISO-B Series, Ball Lock, Brass
Save 20% Save %
$ 250.00
$ 250.00 - $ 250.00
$ 250.00
$ 200.00
$ 200.00 - $ 200.00
$ 200.00

Foster 42-4S/S, 3/8" Industrial Plug x 3/8" Male NPT, 4 Series, 303 Stainless

Reliable, leak-free 3/8" connections for air and fluid lines. The Foster 42-4S/S is a 303 Stainless 3/8" industrial plug from the Foster 4 Series —...

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$ 250.00
$ 250.00 - $ 250.00
$ 250.00
$ 200.00
$ 200.00 - $ 200.00
$ 200.00
Save 20% Save %
Foster BLH1B, 1/8" ISO-B Hydraulic Coupler x 1/8" Female NPT, ISO-B Series, Ball Lock, Brass
Save 20% Save %
$ 155.00
$ 155.00 - $ 155.00
$ 155.00
$ 124.00
$ 124.00 - $ 124.00
$ 124.00

Foster 42-4B, 3/8" Industrial Plug x 3/8" Male NPT, 4 Series, 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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$ 155.00
$ 155.00 - $ 155.00
$ 155.00
$ 124.00
$ 124.00 - $ 124.00
$ 124.00
Save 20% Save %
Foster BLH1B, 1/8" ISO-B Hydraulic Coupler x 1/8" Female NPT, ISO-B Series, Ball Lock, Brass
Save 20% Save %
$ 181.00
$ 181.00 - $ 181.00
$ 181.00
$ 145.00
$ 145.00 - $ 145.00
$ 145.00

Foster 40-4S/S, 3/8" Industrial Plug x 1/4" Male NPT, 4 Series, 303 Stainless

Reliable, leak-free 3/8" connections for air and fluid lines. The Foster 40-4S/S is a 303 Stainless 3/8" industrial plug from the Foster 4 Series —...

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$ 181.00
$ 181.00 - $ 181.00
$ 181.00
$ 145.00
$ 145.00 - $ 145.00
$ 145.00
Save 20% Save %
Foster BLH1B, 1/8" ISO-B Hydraulic Coupler x 1/8" Female NPT, ISO-B Series, Ball Lock, Brass
Save 21% Save %
$ 159.00
$ 159.00 - $ 159.00
$ 159.00
$ 126.00
$ 126.00 - $ 126.00
$ 126.00

Foster 40-4B, 3/8" Industrial Plug x 1/4" Male NPT, 4 Series, 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...

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$ 159.00
$ 159.00 - $ 159.00
$ 159.00
$ 126.00
$ 126.00 - $ 126.00
$ 126.00
Save 21% Save %
Foster BLH1B, 1/8" ISO-B Hydraulic Coupler x 1/8" Female NPT, ISO-B Series, Ball Lock, Brass
Save 20% Save %
$ 93.00
$ 93.00 - $ 93.00
$ 93.00
$ 74.00
$ 74.00 - $ 74.00
$ 74.00

Foster 40-4, 3/8" Industrial Plug x 1/4" Male NPT, 4 Series, 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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$ 93.00
$ 93.00 - $ 93.00
$ 93.00
$ 74.00
$ 74.00 - $ 74.00
$ 74.00
Save 20% Save %
Foster BLH1B, 1/8" ISO-B Hydraulic Coupler x 1/8" Female NPT, ISO-B Series, Ball Lock, Brass
Save 20% Save %
$ 197.00
$ 197.00 - $ 197.00
$ 197.00
$ 157.00
$ 157.00 - $ 157.00
$ 157.00

Foster 38-4, 3/8" Industrial Plug x 1/8" Male NPT, 4 Series, Steel

Reliable, leak-free 3/8" connections for air and fluid lines. The Foster 38-4 is a Steel 3/8" industrial plug from the Foster 4 Series — a high-flo...

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$ 197.00
$ 197.00 - $ 197.00
$ 197.00
$ 157.00
$ 157.00 - $ 157.00
$ 157.00
Save 20% Save %
Foster BLH1B, 1/8" ISO-B Hydraulic Coupler x 1/8" Female NPT, ISO-B Series, Ball Lock, Brass
Save 20% Save %
$ 160.00
$ 160.00 - $ 160.00
$ 160.00
$ 128.00
$ 128.00 - $ 128.00
$ 128.00

Foster 45-4, 3/8" Industrial Plug x 1/2" Female NPT, 4 Series, 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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$ 160.00
$ 160.00 - $ 160.00
$ 160.00
$ 128.00
$ 128.00 - $ 128.00
$ 128.00
Save 20% Save %
Foster BLH1B, 1/8" ISO-B Hydraulic Coupler x 1/8" Female NPT, ISO-B Series, Ball Lock, Brass
Save 20% Save %
$ 334.00
$ 334.00 - $ 334.00
$ 334.00
$ 267.00
$ 267.00 - $ 267.00
$ 267.00

Foster 43-4S/S, 3/8" Industrial Plug x 3/8" Female NPT, 4 Series, 303 Stainless

Reliable, leak-free 3/8" connections for air and fluid lines. The Foster 43-4S/S is a 303 Stainless 3/8" industrial plug from the Foster 4 Series —...

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$ 334.00
$ 334.00 - $ 334.00
$ 334.00
$ 267.00
$ 267.00 - $ 267.00
$ 267.00
Save 20% Save %
Foster BLH1B, 1/8" ISO-B Hydraulic Coupler x 1/8" Female NPT, ISO-B Series, Ball Lock, Brass
Save 20% Save %
$ 116.00
$ 116.00 - $ 116.00
$ 116.00
$ 93.00
$ 93.00 - $ 93.00
$ 93.00

Foster 43-4, 3/8" Industrial Plug x 3/8" Female NPT, 4 Series, 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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$ 116.00
$ 116.00 - $ 116.00
$ 116.00
$ 93.00
$ 93.00 - $ 93.00
$ 93.00
Save 20% Save %
Foster BLH1B, 1/8" ISO-B Hydraulic Coupler x 1/8" Female NPT, ISO-B Series, Ball Lock, Brass
Save 20% Save %
$ 93.00
$ 93.00 - $ 93.00
$ 93.00
$ 74.00
$ 74.00 - $ 74.00
$ 74.00

Foster 41-4, 3/8" Industrial Plug x 1/4" Female NPT, 4 Series, 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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$ 93.00
$ 93.00 - $ 93.00
$ 93.00
$ 74.00
$ 74.00 - $ 74.00
$ 74.00
Save 20% Save %

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