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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 %
$ 264.00
$ 264.00 - $ 264.00
$ 264.00
$ 211.00
$ 211.00 - $ 211.00
$ 211.00

Foster PB5-4, 3/8" Industrial Plug x Reusable Hose Fitting, 1/4" ID x 9/16" OD, 4 Series, Steel

Reliable, leak-free 3/8" connections for air and fluid lines. The Foster PB5-4 is a Steel 3/8" industrial plug from the Foster 4 Series — a high-fl...

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$ 264.00
$ 264.00 - $ 264.00
$ 264.00
$ 211.00
$ 211.00 - $ 211.00
$ 211.00
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Foster BLH1B, 1/8" ISO-B Hydraulic Coupler x 1/8" Female NPT, ISO-B Series, Ball Lock, Brass Save 20% Save %
$ 283.00
$ 283.00 - $ 283.00
$ 283.00
$ 226.00
$ 226.00 - $ 226.00
$ 226.00

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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$ 283.00
$ 283.00 - $ 283.00
$ 283.00
$ 226.00
$ 226.00 - $ 226.00
$ 226.00
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Foster BLH1B, 1/8" ISO-B Hydraulic Coupler x 1/8" Female NPT, ISO-B Series, Ball Lock, Brass Save 20% Save %
$ 205.00
$ 205.00 - $ 205.00
$ 205.00
$ 165.00
$ 165.00 - $ 165.00
$ 165.00

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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$ 205.00
$ 205.00 - $ 205.00
$ 205.00
$ 165.00
$ 165.00 - $ 165.00
$ 165.00
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Foster BLH1B, 1/8" ISO-B Hydraulic Coupler x 1/8" Female NPT, ISO-B Series, Ball Lock, Brass Save 20% Save %
$ 511.00
$ 511.00 - $ 511.00
$ 511.00
$ 408.00
$ 408.00 - $ 408.00
$ 408.00

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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$ 511.00
$ 511.00 - $ 511.00
$ 511.00
$ 408.00
$ 408.00 - $ 408.00
$ 408.00
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Foster BLH1B, 1/8" ISO-B Hydraulic Coupler x 1/8" Female NPT, ISO-B Series, Ball Lock, Brass
Save 20% Save %
$ 122.00
$ 122.00 - $ 122.00
$ 122.00
$ 97.00
$ 97.00 - $ 97.00
$ 97.00

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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$ 122.00
$ 122.00 - $ 122.00
$ 122.00
$ 97.00
$ 97.00 - $ 97.00
$ 97.00
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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 %
$ 141.00
$ 141.00 - $ 141.00
$ 141.00
$ 114.00
$ 114.00 - $ 114.00
$ 114.00

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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$ 141.00
$ 141.00 - $ 141.00
$ 141.00
$ 114.00
$ 114.00 - $ 114.00
$ 114.00
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 %
$ 133.00
$ 133.00 - $ 133.00
$ 133.00
$ 107.00
$ 107.00 - $ 107.00
$ 107.00

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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$ 133.00
$ 133.00 - $ 133.00
$ 133.00
$ 107.00
$ 107.00 - $ 107.00
$ 107.00
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 %
$ 188.00
$ 188.00 - $ 188.00
$ 188.00
$ 152.00
$ 152.00 - $ 152.00
$ 152.00

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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$ 188.00
$ 188.00 - $ 188.00
$ 188.00
$ 152.00
$ 152.00 - $ 152.00
$ 152.00
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 %
$ 120.00
$ 120.00 - $ 120.00
$ 120.00
$ 95.00
$ 95.00 - $ 95.00
$ 95.00

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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$ 120.00
$ 120.00 - $ 120.00
$ 120.00
$ 95.00
$ 95.00 - $ 95.00
$ 95.00
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 %
$ 198.00
$ 198.00 - $ 198.00
$ 198.00
$ 158.00
$ 158.00 - $ 158.00
$ 158.00

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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$ 198.00
$ 198.00 - $ 198.00
$ 198.00
$ 158.00
$ 158.00 - $ 158.00
$ 158.00
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 %
$ 167.00
$ 167.00 - $ 167.00
$ 167.00
$ 133.00
$ 133.00 - $ 133.00
$ 133.00

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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$ 167.00
$ 167.00 - $ 167.00
$ 167.00
$ 133.00
$ 133.00 - $ 133.00
$ 133.00
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 %
$ 327.00
$ 327.00 - $ 327.00
$ 327.00
$ 260.00
$ 260.00 - $ 260.00
$ 260.00

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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$ 327.00
$ 327.00 - $ 327.00
$ 327.00
$ 260.00
$ 260.00 - $ 260.00
$ 260.00
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 %
$ 247.00
$ 247.00 - $ 247.00
$ 247.00
$ 198.00
$ 198.00 - $ 198.00
$ 198.00

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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$ 247.00
$ 247.00 - $ 247.00
$ 247.00
$ 198.00
$ 198.00 - $ 198.00
$ 198.00
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 %
$ 382.00
$ 382.00 - $ 382.00
$ 382.00
$ 306.00
$ 306.00 - $ 306.00
$ 306.00

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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$ 382.00
$ 382.00 - $ 382.00
$ 382.00
$ 306.00
$ 306.00 - $ 306.00
$ 306.00
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 %
$ 133.00
$ 133.00 - $ 133.00
$ 133.00
$ 107.00
$ 107.00 - $ 107.00
$ 107.00

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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$ 133.00
$ 133.00 - $ 133.00
$ 133.00
$ 107.00
$ 107.00 - $ 107.00
$ 107.00
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 %
$ 275.00
$ 275.00 - $ 275.00
$ 275.00
$ 220.00
$ 220.00 - $ 220.00
$ 220.00

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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$ 275.00
$ 275.00 - $ 275.00
$ 275.00
$ 220.00
$ 220.00 - $ 220.00
$ 220.00
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 %
$ 171.00
$ 171.00 - $ 171.00
$ 171.00
$ 137.00
$ 137.00 - $ 137.00
$ 137.00

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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$ 171.00
$ 171.00 - $ 171.00
$ 171.00
$ 137.00
$ 137.00 - $ 137.00
$ 137.00
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 %
$ 200.00
$ 200.00 - $ 200.00
$ 200.00
$ 160.00
$ 160.00 - $ 160.00
$ 160.00

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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$ 200.00
$ 200.00 - $ 200.00
$ 200.00
$ 160.00
$ 160.00 - $ 160.00
$ 160.00
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 %
$ 175.00
$ 175.00 - $ 175.00
$ 175.00
$ 139.00
$ 139.00 - $ 139.00
$ 139.00

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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$ 175.00
$ 175.00 - $ 175.00
$ 175.00
$ 139.00
$ 139.00 - $ 139.00
$ 139.00
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 %
$ 103.00
$ 103.00 - $ 103.00
$ 103.00
$ 82.00
$ 82.00 - $ 82.00
$ 82.00

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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$ 103.00
$ 103.00 - $ 103.00
$ 103.00
$ 82.00
$ 82.00 - $ 82.00
$ 82.00
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 %
$ 217.00
$ 217.00 - $ 217.00
$ 217.00
$ 173.00
$ 173.00 - $ 173.00
$ 173.00

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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$ 217.00
$ 217.00 - $ 217.00
$ 217.00
$ 173.00
$ 173.00 - $ 173.00
$ 173.00
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 %
$ 177.00
$ 177.00 - $ 177.00
$ 177.00
$ 141.00
$ 141.00 - $ 141.00
$ 141.00

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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$ 177.00
$ 177.00 - $ 177.00
$ 177.00
$ 141.00
$ 141.00 - $ 141.00
$ 141.00
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 %
$ 368.00
$ 368.00 - $ 368.00
$ 368.00
$ 294.00
$ 294.00 - $ 294.00
$ 294.00

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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$ 368.00
$ 368.00 - $ 368.00
$ 368.00
$ 294.00
$ 294.00 - $ 294.00
$ 294.00
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 %
$ 127.00
$ 127.00 - $ 127.00
$ 127.00
$ 103.00
$ 103.00 - $ 103.00
$ 103.00

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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$ 127.00
$ 127.00 - $ 127.00
$ 127.00
$ 103.00
$ 103.00 - $ 103.00
$ 103.00
Save 19% Save %

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