Dorman Vacuum Caps: Small Line Sizes vs Bypass Caps

Small vacuum hoses and larger bypass fittings can both end in an unused port that needs a correctly sized closure. Dorman's HELP! and OE Solutions product lines include rubber and vinyl caps in different diameter ranges. A cap that appears similar may be too small, too loose or unsuitable for the fluid and temperature involved. Identify the original application and required size before ordering.

Small vacuum caps versus larger bypass caps

Dorman cap kit comparison by exact MPN

The chart gives the manufacturer-described assortment ranges, not a guarantee of fit on a particular vehicle. For multi-size kits, the quantity in each individual diameter should be confirmed from the packaging when that breakdown matters.

How to match a replacement cap

1. Identify what the port does. A vacuum-control nipple, coolant bypass fitting, fuel-system port and brake or emissions connection are not automatically suitable for the same cap material.
2. Measure the fitting. Compare the port's outside diameter with the cap's listed nominal size; don't judge the opening by eye.
3. Check the environment. Verify the cap's compatibility with expected temperature, pressure or vacuum and any chemicals or fluids, using the application's service information.
4. Inspect the retaining surface. A cracked or corroded nipple can prevent a good seal even with the correct cap.
5. Verify that the port may be sealed. Do not cap a required vent, drain, vacuum sensor, emissions device, cooling or fuel return connection simply because it is open.

Frequently asked questions

Is a 5/8-inch bypass cap interchangeable with a 5/8-inch vacuum cap? A matching nominal diameter is not enough by itself. Fit, material, environment and intended use must all agree.

Are Dorman 41050 and 47388 equivalent kits? They list the same six nominal small-size options, but 41050 has eight pieces while 47388 contains thirty. Verify the assortment counts when you need a specific quantity.

Does 47397 provide the same material as 47388? No. The 47397 assortment is vinyl, while 47388 is described as black rubber.

Compare Dorman rubber and vinyl cap listings

Open the matching MPN to check current availability, item condition and actual contents. Catalog photographs identify the product family and do not establish the cosmetic condition of an individual item.

Dorman 02252 · Large rubber bypass caps

5/8 in nominal sizes; 2-piece package. Black rubber.

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Dorman 02253 · Mixed rubber bypass caps

3/8, 1/2, 5/8, 3/4 in nominal sizes; 8-piece package. Black rubber.

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Dorman 02254 · Large rubber bypass caps

3/4 in nominal sizes; 2-piece package. Black rubber.

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Dorman 41050 · Rubber vacuum cap assortment

5/32, 3/16, 7/32, 1/4, 5/16, 3/8 in nominal sizes; 8-piece package. Black rubber.

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Dorman 47388 · Rubber vacuum cap assortment

5/32, 3/16, 7/32, 1/4, 5/16, 3/8 in nominal sizes; 30-piece package. Black rubber.

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Dorman 47389 · Single-size rubber vacuum caps

1/8 in nominal sizes; 5-piece package. Black rubber.

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Dorman 47391 · Single-size rubber vacuum caps

3/16 in nominal sizes; 5-piece package. Black rubber.

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Dorman 47397 · Coloured vinyl vacuum caps

1/8, 3/16, 1/4, 5/16, 3/8 in nominal sizes; 20-piece package. Yellow, blue, red, white and black vinyl.

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Other vehicle hardware reference pages

For related engine-service hardware, our Dorman exhaust stud size guide compares metric and inch threads. Exhaust fasteners and vacuum caps are separate repair categories, so identify each by its own original part number.