Skip to content
☀️ Take an Additional 10% Off Your Entire Order with code GEARUP10 at checkout.
☀️ Additional 10% Off • GEARUP10

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.

Filters

Foster BLH1B, 1/8" ISO-B Hydraulic Coupler x 1/8" Female NPT, ISO-B Series, Ball Lock, Brass Save 20% Save %
$ 783.00
$ 783.00 - $ 783.00
$ 783.00
$ 627.00
$ 627.00 - $ 627.00
$ 627.00

Foster SLSD13-4, 3/8" Industrial Coupler x Reusable Hose Fitting, 3/8" ID x 13/16" OD, 4 Series, Automatic Sleeve Lock, Brass

Reliable, leak-free 3/8" connections for air and fluid lines. The Foster SLSD13-4 is a Brass 3/8" industrial coupler from the Foster 4 Series — a h...

View full details
$ 783.00
$ 783.00 - $ 783.00
$ 783.00
$ 627.00
$ 627.00 - $ 627.00
$ 627.00
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 %
$ 685.00
$ 685.00 - $ 685.00
$ 685.00
$ 549.00
$ 549.00 - $ 549.00
$ 549.00

Foster FMSD13-4, 3/8" Industrial Coupler x Reusable Hose Fitting, 3/8" ID x 13/16" OD, 4 Series, Automatic, Brass

Reliable, leak-free 3/8" connections for air and fluid lines. The Foster FMSD13-4 is a Brass 3/8" industrial coupler from the Foster 4 Series — a h...

View full details
$ 685.00
$ 685.00 - $ 685.00
$ 685.00
$ 549.00
$ 549.00 - $ 549.00
$ 549.00
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 %
$ 776.00
$ 776.00 - $ 776.00
$ 776.00
$ 622.00
$ 622.00 - $ 622.00
$ 622.00

Foster SLSD11-4, 3/8" Industrial Coupler x Reusable Hose Fitting, 3/8" ID x 3/4" OD, 4 Series, Automatic Sleeve Lock, Brass

Reliable, leak-free 3/8" connections for air and fluid lines. The Foster SLSD11-4 is a Brass 3/8" industrial coupler from the Foster 4 Series — a h...

View full details
$ 776.00
$ 776.00 - $ 776.00
$ 776.00
$ 622.00
$ 622.00 - $ 622.00
$ 622.00
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 %
$ 675.00
$ 675.00 - $ 675.00
$ 675.00
$ 540.00
$ 540.00 - $ 540.00
$ 540.00

Foster FMSD11-4, 3/8" Industrial Coupler x Reusable Hose Fitting, 3/8" ID x 3/4" OD, 4 Series, Automatic, Brass

Reliable, leak-free 3/8" connections for air and fluid lines. The Foster FMSD11-4 is a Brass 3/8" industrial coupler from the Foster 4 Series — a h...

View full details
$ 675.00
$ 675.00 - $ 675.00
$ 675.00
$ 540.00
$ 540.00 - $ 540.00
$ 540.00
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 %
$ 765.00
$ 765.00 - $ 765.00
$ 765.00
$ 611.00
$ 611.00 - $ 611.00
$ 611.00

Foster SLSD9-4, 3/8" Industrial Coupler x Reusable Hose Fitting, 3/8" ID x 11/16" OD, 4 Series, Automatic Sleeve Lock, Brass

Reliable, leak-free 3/8" connections for air and fluid lines. The Foster SLSD9-4 is a Brass 3/8" industrial coupler from the Foster 4 Series — a hi...

View full details
$ 765.00
$ 765.00 - $ 765.00
$ 765.00
$ 611.00
$ 611.00 - $ 611.00
$ 611.00
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 %
$ 664.00
$ 664.00 - $ 664.00
$ 664.00
$ 531.00
$ 531.00 - $ 531.00
$ 531.00

Foster FMSD9-4, 3/8" Industrial Coupler x Reusable Hose Fitting, 3/8" ID x 11/16" OD, 4 Series, Automatic, Brass

Reliable, leak-free 3/8" connections for air and fluid lines. The Foster FMSD9-4 is a Brass 3/8" industrial coupler from the Foster 4 Series — a hi...

View full details
$ 664.00
$ 664.00 - $ 664.00
$ 664.00
$ 531.00
$ 531.00 - $ 531.00
$ 531.00
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 %
$ 753.00
$ 753.00 - $ 753.00
$ 753.00
$ 602.00
$ 602.00 - $ 602.00
$ 602.00

Foster SLSD7-4, 3/8" Industrial Coupler x Reusable Hose Fitting, 3/8" ID x 5/8" OD, 4 Series, Automatic Sleeve Lock, Brass

Reliable, leak-free 3/8" connections for air and fluid lines. The Foster SLSD7-4 is a Brass 3/8" industrial coupler from the Foster 4 Series — a hi...

View full details
$ 753.00
$ 753.00 - $ 753.00
$ 753.00
$ 602.00
$ 602.00 - $ 602.00
$ 602.00
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 %
$ 892.00
$ 892.00 - $ 892.00
$ 892.00
$ 714.00
$ 714.00 - $ 714.00
$ 714.00

Foster FMSD7-4, 3/8" Industrial Coupler x Reusable Hose Fitting, 3/8" ID x 5/8" OD, 4 Series, Automatic, Brass

Reliable, leak-free 3/8" connections for air and fluid lines. The Foster FMSD7-4 is a Brass 3/8" industrial coupler from the Foster 4 Series — a hi...

View full details
$ 892.00
$ 892.00 - $ 892.00
$ 892.00
$ 714.00
$ 714.00 - $ 714.00
$ 714.00
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 %
$ 753.00
$ 753.00 - $ 753.00
$ 753.00
$ 602.00
$ 602.00 - $ 602.00
$ 602.00

Foster SLSB7-4, 3/8" Industrial Coupler x Reusable Hose Fitting, 1/4" ID x 5/8" OD, 4 Series, Automatic Sleeve Lock, Brass

Reliable, leak-free 3/8" connections for air and fluid lines. The Foster SLSB7-4 is a Brass 3/8" industrial coupler from the Foster 4 Series — a hi...

View full details
$ 753.00
$ 753.00 - $ 753.00
$ 753.00
$ 602.00
$ 602.00 - $ 602.00
$ 602.00
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 %
$ 678.00
$ 678.00 - $ 678.00
$ 678.00
$ 542.00
$ 542.00 - $ 542.00
$ 542.00

Foster FMSB7-4, 3/8" Industrial Coupler x Reusable Hose Fitting, 1/4" ID x 5/8" OD, 4 Series, Automatic, Brass

Reliable, leak-free 3/8" connections for air and fluid lines. The Foster FMSB7-4 is a Brass 3/8" industrial coupler from the Foster 4 Series — a hi...

View full details
$ 678.00
$ 678.00 - $ 678.00
$ 678.00
$ 542.00
$ 542.00 - $ 542.00
$ 542.00
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 %
$ 745.00
$ 745.00 - $ 745.00
$ 745.00
$ 597.00
$ 597.00 - $ 597.00
$ 597.00

Foster SLSB5-4, 3/8" Industrial Coupler x Reusable Hose Fitting, 1/4" ID x 9/16" OD, 4 Series, Automatic Sleeve Lock, Brass

Reliable, leak-free 3/8" connections for air and fluid lines. The Foster SLSB5-4 is a Brass 3/8" industrial coupler from the Foster 4 Series — a hi...

View full details
$ 745.00
$ 745.00 - $ 745.00
$ 745.00
$ 597.00
$ 597.00 - $ 597.00
$ 597.00
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 %
$ 671.00
$ 671.00 - $ 671.00
$ 671.00
$ 537.00
$ 537.00 - $ 537.00
$ 537.00

Foster FMSB5-4, 3/8" Industrial Coupler x Reusable Hose Fitting, 1/4" ID x 9/16" OD, 4 Series, Automatic, Brass

Reliable, leak-free 3/8" connections for air and fluid lines. The Foster FMSB5-4 is a Brass 3/8" industrial coupler from the Foster 4 Series — a hi...

View full details
$ 671.00
$ 671.00 - $ 671.00
$ 671.00
$ 537.00
$ 537.00 - $ 537.00
$ 537.00
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 %
$ 701.00
$ 701.00 - $ 701.00
$ 701.00
$ 561.00
$ 561.00 - $ 561.00
$ 561.00

Foster SLSB3-4, 3/8" Industrial Coupler x Reusable Hose Fitting, 1/4" ID x 1/2" OD, 4 Series, Automatic Sleeve Lock, Brass

Reliable, leak-free 3/8" connections for air and fluid lines. The Foster SLSB3-4 is a Brass 3/8" industrial coupler from the Foster 4 Series — a hi...

View full details
$ 701.00
$ 701.00 - $ 701.00
$ 701.00
$ 561.00
$ 561.00 - $ 561.00
$ 561.00
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 %
$ 630.00
$ 630.00 - $ 630.00
$ 630.00
$ 505.00
$ 505.00 - $ 505.00
$ 505.00

Foster FMSB3-4, 3/8" Industrial Coupler x Reusable Hose Fitting, 1/4" ID x 1/2" OD, 4 Series, Automatic, Brass

Reliable, leak-free 3/8" connections for air and fluid lines. The Foster FMSB3-4 is a Brass 3/8" industrial coupler from the Foster 4 Series — a hi...

View full details
$ 630.00
$ 630.00 - $ 630.00
$ 630.00
$ 505.00
$ 505.00 - $ 505.00
$ 505.00
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 %
$ 707.00
$ 707.00 - $ 707.00
$ 707.00
$ 567.00
$ 567.00 - $ 567.00
$ 567.00

Foster FM1814W, 3/8" Industrial Coupler x 1/2" Push-On Hose Stem, 4 Series, Automatic, Water, Brass/SS

Reliable, leak-free 3/8" connections for air and fluid lines. The Foster FM1814W is a Brass/SS 3/8" industrial coupler from the Foster 4 Series — a...

View full details
$ 707.00
$ 707.00 - $ 707.00
$ 707.00
$ 567.00
$ 567.00 - $ 567.00
$ 567.00
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 %
$ 738.00
$ 738.00 - $ 738.00
$ 738.00
$ 591.00
$ 591.00 - $ 591.00
$ 591.00

Foster SL1814, 3/8" Industrial Coupler x 1/2" Push-On Hose Stem, 4 Series, Automatic Sleeve Lock, Brass

Reliable, leak-free 3/8" connections for air and fluid lines. The Foster SL1814 is a Brass 3/8" industrial coupler from the Foster 4 Series — a hig...

View full details
$ 738.00
$ 738.00 - $ 738.00
$ 738.00
$ 591.00
$ 591.00 - $ 591.00
$ 591.00
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 %
$ 636.00
$ 636.00 - $ 636.00
$ 636.00
$ 508.00
$ 508.00 - $ 508.00
$ 508.00

Foster FM1814, 3/8" Industrial Coupler x 1/2" Push-On Hose Stem, 4 Series, Automatic, Brass

Reliable, leak-free 3/8" connections for air and fluid lines. The Foster FM1814 is a Brass 3/8" industrial coupler from the Foster 4 Series — a hig...

View full details
$ 636.00
$ 636.00 - $ 636.00
$ 636.00
$ 508.00
$ 508.00 - $ 508.00
$ 508.00
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 %
$ 721.00
$ 721.00 - $ 721.00
$ 721.00
$ 576.00
$ 576.00 - $ 576.00
$ 576.00

Foster SL1714, 3/8" Industrial Coupler x 3/8" Push-On Hose Stem, 4 Series, Automatic Sleeve Lock, Brass

Reliable, leak-free 3/8" connections for air and fluid lines. The Foster SL1714 is a Brass 3/8" industrial coupler from the Foster 4 Series — a hig...

View full details
$ 721.00
$ 721.00 - $ 721.00
$ 721.00
$ 576.00
$ 576.00 - $ 576.00
$ 576.00
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 %
$ 616.00
$ 616.00 - $ 616.00
$ 616.00
$ 494.00
$ 494.00 - $ 494.00
$ 494.00

Foster FM1714, 3/8" Industrial Coupler x 3/8" Push-On Hose Stem, 4 Series, Automatic, 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...

View full details
$ 616.00
$ 616.00 - $ 616.00
$ 616.00
$ 494.00
$ 494.00 - $ 494.00
$ 494.00
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 %
$ 684.00
$ 684.00 - $ 684.00
$ 684.00
$ 545.00
$ 545.00 - $ 545.00
$ 545.00

Foster FM4904W, 3/8" Industrial Coupler x 1/2" Hose ID, 4 Series, Automatic, Water, Brass/SS

Reliable, leak-free 3/8" connections for air and fluid lines. The Foster FM4904W is a Brass/SS 3/8" industrial coupler from the Foster 4 Series — a...

View full details
$ 684.00
$ 684.00 - $ 684.00
$ 684.00
$ 545.00
$ 545.00 - $ 545.00
$ 545.00
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 %
$ 685.00
$ 685.00 - $ 685.00
$ 685.00
$ 549.00
$ 549.00 - $ 549.00
$ 549.00

Foster SL4904, 3/8" Industrial Coupler x 1/2" Hose ID, 4 Series, Automatic Sleeve Lock, Brass

Reliable, leak-free 3/8" connections for air and fluid lines. The Foster SL4904 is a Brass 3/8" industrial coupler from the Foster 4 Series — a hig...

View full details
$ 685.00
$ 685.00 - $ 685.00
$ 685.00
$ 549.00
$ 549.00 - $ 549.00
$ 549.00
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 %
$ 588.00
$ 588.00 - $ 588.00
$ 588.00
$ 471.00
$ 471.00 - $ 471.00
$ 471.00

Foster FM4904, 3/8" Industrial Coupler x 1/2" Hose ID, 4 Series, Automatic, 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...

View full details
$ 588.00
$ 588.00 - $ 588.00
$ 588.00
$ 471.00
$ 471.00 - $ 471.00
$ 471.00
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 %
$ 650.00
$ 650.00 - $ 650.00
$ 650.00
$ 519.00
$ 519.00 - $ 519.00
$ 519.00

Foster FM4804W, 3/8" Industrial Coupler x 3/8" Hose ID, 4 Series, Automatic, Water, Brass/SS

Reliable, leak-free 3/8" connections for air and fluid lines. The Foster FM4804W is a Brass/SS 3/8" industrial coupler from the Foster 4 Series — a...

View full details
$ 650.00
$ 650.00 - $ 650.00
$ 650.00
$ 519.00
$ 519.00 - $ 519.00
$ 519.00
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 %
$ 613.00
$ 613.00 - $ 613.00
$ 613.00
$ 491.00
$ 491.00 - $ 491.00
$ 491.00

Foster FM4804H, 3/8" Industrial Coupler x 3/8" Hose ID, 4 Series, Automatic, Heat/Viton, Brass

Reliable, leak-free 3/8" connections for air and fluid lines. The Foster FM4804H is a Brass 3/8" industrial coupler from the Foster 4 Series — a hi...

View full details
$ 613.00
$ 613.00 - $ 613.00
$ 613.00
$ 491.00
$ 491.00 - $ 491.00
$ 491.00
Save 20% Save %

Request a Quote

Bulk and dealer pricing. Tell us what you need and we’ll reply within one business day.