Question 1

What is a NAPA 4003 fuel filter and how is it related to WIX 24003?

Accepted Answer

The NAPA 4003 is a high-flow inline fuel filter rated around 12 GPM, commonly used on fuel transfer pumps and automotive applications. WIX 24003 is the equivalent WIX-number part with the same dimensions and thread pattern. On napafuelfilter.com, the NAPA 4003 / WIX 24003 housing is repurposed as the outer tube for modular solvent trap kits (aluminum or stainless steel, 6"–12"), because its 1.375×24 HUB thread and 1/2-28 & 5/8-24 adapter compatibility make it a popular platform for firearm cleaning accessories.

Question 2

What is a solvent trap and how does it work?

Accepted Answer

A solvent trap is a muzzle-threaded accessory for firearm cleaning. It screws onto the barrel (like a muzzle brake) and uses internal cup-shaped baffles to catch solvent, oil, and debris so they don't run back into the action. Our NAPA 4003-based kits are modular—you can add or remove cups (6, 8, 10 cups depending on length) and choose between C-cell (~1.3" OD) and D-cell (~1.65" OD) diameters to match your setup.

Question 3

What thread patterns are compatible with your NAPA 4003 solvent trap kits?

Accepted Answer

All our NAPA 4003 / WIX 24003 solvent trap tubes come with 1.375×24 HUB threading on the main body. We include adapter spacers for the two most common barrel threads: 1/2-28 (common on .22, 5.56, 9mm) and 5/8-24 (common on .308, 7.62, 6.5 Creedmoor). If you're unsure of your barrel thread, check your barrel manufacturer specs before ordering.

Question 4

Aluminum vs Stainless Steel — which NAPA 4003 solvent trap should I choose?

Accepted Answer

6061 or 7075 Aluminum is lighter, easier to handle, and more affordable—great for range-day cleaning and DIY drilling practice. Stainless steel is heavier, more corrosion-resistant, and holds up better if you plan to convert the unit (with ATF approval). For pure solvent-catch use, aluminum is the popular pick; for long-term durability, go stainless.

Question 5

How many cups do I need in my solvent trap?

Accepted Answer

It depends on tube length and intended use: 6" tube → typically 6–7 cups, best for pistols / rimfire; 8.5"–10" tube → 6–10 cups, good balance for rifle calibers; 12" tube → maximum cup count, deeper stack for larger volumes. More cups mean more surface area to catch solvent, but also longer overall length—check your barrel clearance (sights, handguard) before going long.

Question 6

Is it legal to own or convert a NAPA 4003 fuel filter / solvent trap into a suppressor?

Accepted Answer

In the US, the NAPA 4003 / WIX 24003 housing itself is sold here as a fuel filter / solvent trap maintenance accessory. Converting it into a suppressor (by drilling end caps, etc.) requires you to: 1) File ATF Form 1, 2) Pay the $200 tax stamp, 3) Wait for approval before making any modifications. Possession of a drilled/convertible unit without ATF approval is a federal felony. Our products ship as closed-end, undrilled solvent traps or fuel filters. We do not provide instructions for suppressor conversion. Always check your state/local laws—some states prohibit suppressors entirely even with a tax stamp.

Question 7

Do I need a drilling jig for the NAPA 4003 solvent trap?

Accepted Answer

If you plan to machine the end caps after receiving ATF Form 1 approval, yes—a modular solvent trap drilling jig (1.375×24 cup jig) keeps the hole centered and prevents ruining the tube threads. A dedicated jig that indexes off the HUB threads ensures each cup stacks true. For users who only want the solvent-catch function, no drilling is needed—the unit ships ready to thread on.

Question 8

Can the NAPA 4003 still be used as an actual vehicle fuel filter?

Accepted Answer

Yes. The base NAPA 4003 / WIX 24003 is a real inline fuel filter (~10 μm filtration, ~12 GPM flow) used on fuel transfer pumps, tractors, and some automotive returns. Our site sells the tube + cups + adapters as a solvent-trap kit, but the NAPA 4003 shell itself is the same PN you'd buy at a parts store. Note: once assembled as a solvent trap with cups inside, it's no longer suitable for fuel duty.

Question 9

How do I clean and maintain a stainless steel NAPA 4003 solvent trap?

Accepted Answer

After a cleaning session: (1) unscrew the HUB end cap, (2) slide out cups, (3) pour collected solvent into a disposal container, (4) wipe cups with shop towel, (5) rinse with brake cleaner or mineral spirits if gummy. Stainless cups can be soaked in a solvent tank; for aluminum cups avoid harsh acidic dips that etch. Reassemble finger-tight—don't over-torque the HUB threads.

Question 10

Do you ship NAPA 4003 solvent trap kits to the US?

Accepted Answer

Yes—US stock, fast shipping from a domestic warehouse. Orders ship via USPS/UPS depending on weight. Because this category receives extra scrutiny, we only ship to US addresses and will cancel orders that look like export/re-shipping to protect both parties from customs/legal issues.

Shipping Policy