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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 19% Save %
$ 191.00
$ 191.00 - $ 191.00
$ 191.00
$ 154.00
$ 154.00 - $ 154.00
$ 154.00

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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$ 191.00
$ 191.00 - $ 191.00
$ 191.00
$ 154.00
$ 154.00 - $ 154.00
$ 154.00
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 %
$ 476.00
$ 476.00 - $ 476.00
$ 476.00
$ 381.00
$ 381.00 - $ 381.00
$ 381.00

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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$ 476.00
$ 476.00 - $ 476.00
$ 476.00
$ 381.00
$ 381.00 - $ 381.00
$ 381.00
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 %
$ 114.00
$ 114.00 - $ 114.00
$ 114.00
$ 91.00
$ 91.00 - $ 91.00
$ 91.00

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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$ 114.00
$ 114.00 - $ 114.00
$ 114.00
$ 91.00
$ 91.00 - $ 91.00
$ 91.00
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 %
$ 131.00
$ 131.00 - $ 131.00
$ 131.00
$ 106.00
$ 106.00 - $ 106.00
$ 106.00

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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$ 131.00
$ 131.00 - $ 131.00
$ 131.00
$ 106.00
$ 106.00 - $ 106.00
$ 106.00
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 %
$ 124.00
$ 124.00 - $ 124.00
$ 124.00
$ 99.00
$ 99.00 - $ 99.00
$ 99.00

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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$ 124.00
$ 124.00 - $ 124.00
$ 124.00
$ 99.00
$ 99.00 - $ 99.00
$ 99.00
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 %
$ 175.00
$ 175.00 - $ 175.00
$ 175.00
$ 142.00
$ 142.00 - $ 142.00
$ 142.00

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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$ 175.00
$ 175.00 - $ 175.00
$ 175.00
$ 142.00
$ 142.00 - $ 142.00
$ 142.00
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 %
$ 112.00
$ 112.00 - $ 112.00
$ 112.00
$ 89.00
$ 89.00 - $ 89.00
$ 89.00

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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$ 112.00
$ 112.00 - $ 112.00
$ 112.00
$ 89.00
$ 89.00 - $ 89.00
$ 89.00
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 %
$ 184.00
$ 184.00 - $ 184.00
$ 184.00
$ 147.00
$ 147.00 - $ 147.00
$ 147.00

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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$ 184.00
$ 184.00 - $ 184.00
$ 184.00
$ 147.00
$ 147.00 - $ 147.00
$ 147.00
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 %
$ 156.00
$ 156.00 - $ 156.00
$ 156.00
$ 124.00
$ 124.00 - $ 124.00
$ 124.00

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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$ 156.00
$ 156.00 - $ 156.00
$ 156.00
$ 124.00
$ 124.00 - $ 124.00
$ 124.00
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 %
$ 305.00
$ 305.00 - $ 305.00
$ 305.00
$ 243.00
$ 243.00 - $ 243.00
$ 243.00

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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$ 305.00
$ 305.00 - $ 305.00
$ 305.00
$ 243.00
$ 243.00 - $ 243.00
$ 243.00
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 %
$ 230.00
$ 230.00 - $ 230.00
$ 230.00
$ 184.00
$ 184.00 - $ 184.00
$ 184.00

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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$ 230.00
$ 230.00 - $ 230.00
$ 230.00
$ 184.00
$ 184.00 - $ 184.00
$ 184.00
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 %
$ 356.00
$ 356.00 - $ 356.00
$ 356.00
$ 285.00
$ 285.00 - $ 285.00
$ 285.00

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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$ 356.00
$ 356.00 - $ 356.00
$ 356.00
$ 285.00
$ 285.00 - $ 285.00
$ 285.00
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 %
$ 124.00
$ 124.00 - $ 124.00
$ 124.00
$ 99.00
$ 99.00 - $ 99.00
$ 99.00

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...

View full details
$ 124.00
$ 124.00 - $ 124.00
$ 124.00
$ 99.00
$ 99.00 - $ 99.00
$ 99.00
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 %
$ 257.00
$ 257.00 - $ 257.00
$ 257.00
$ 206.00
$ 206.00 - $ 206.00
$ 206.00

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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$ 257.00
$ 257.00 - $ 257.00
$ 257.00
$ 206.00
$ 206.00 - $ 206.00
$ 206.00
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 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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$ 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 %
$ 89.00
$ 89.00 - $ 89.00
$ 89.00
$ 71.00
$ 71.00 - $ 71.00
$ 71.00

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

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

View full details
$ 89.00
$ 89.00 - $ 89.00
$ 89.00
$ 71.00
$ 71.00 - $ 71.00
$ 71.00
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 %
$ 186.00
$ 186.00 - $ 186.00
$ 186.00
$ 149.00
$ 149.00 - $ 149.00
$ 149.00

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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$ 186.00
$ 186.00 - $ 186.00
$ 186.00
$ 149.00
$ 149.00 - $ 149.00
$ 149.00
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 %
$ 163.00
$ 163.00 - $ 163.00
$ 163.00
$ 129.00
$ 129.00 - $ 129.00
$ 129.00

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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$ 163.00
$ 163.00 - $ 163.00
$ 163.00
$ 129.00
$ 129.00 - $ 129.00
$ 129.00
Save 21% Save %
Foster BLH1B, 1/8" ISO-B Hydraulic Coupler x 1/8" Female NPT, ISO-B Series, Ball Lock, Brass
Save 21% Save %
$ 96.00
$ 96.00 - $ 96.00
$ 96.00
$ 76.00
$ 76.00 - $ 76.00
$ 76.00

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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$ 96.00
$ 96.00 - $ 96.00
$ 96.00
$ 76.00
$ 76.00 - $ 76.00
$ 76.00
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 %
$ 202.00
$ 202.00 - $ 202.00
$ 202.00
$ 161.00
$ 161.00 - $ 161.00
$ 161.00

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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$ 202.00
$ 202.00 - $ 202.00
$ 202.00
$ 161.00
$ 161.00 - $ 161.00
$ 161.00
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 %
$ 165.00
$ 165.00 - $ 165.00
$ 165.00
$ 131.00
$ 131.00 - $ 131.00
$ 131.00

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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$ 165.00
$ 165.00 - $ 165.00
$ 165.00
$ 131.00
$ 131.00 - $ 131.00
$ 131.00
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 %
$ 344.00
$ 344.00 - $ 344.00
$ 344.00
$ 275.00
$ 275.00 - $ 275.00
$ 275.00

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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$ 344.00
$ 344.00 - $ 344.00
$ 344.00
$ 275.00
$ 275.00 - $ 275.00
$ 275.00
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 %
$ 119.00
$ 119.00 - $ 119.00
$ 119.00
$ 96.00
$ 96.00 - $ 96.00
$ 96.00

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...

View full details
$ 119.00
$ 119.00 - $ 119.00
$ 119.00
$ 96.00
$ 96.00 - $ 96.00
$ 96.00
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 %
$ 96.00
$ 96.00 - $ 96.00
$ 96.00
$ 76.00
$ 76.00 - $ 76.00
$ 76.00

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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$ 96.00
$ 96.00 - $ 96.00
$ 96.00
$ 76.00
$ 76.00 - $ 76.00
$ 76.00
Save 21% Save %

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