NAPA Gold 1381 vs Baldwin B421: Oil Filter Compatibility
Compare NAPA Gold 1381 and Baldwin B421 oil filters by compatibility, dimensions, thread size, gasket fit, bypass valve, anti-drainback valve status, and match confidence. Use this comparison as a fitment review, not as an automatic substitution guarantee. Both use a M20x1.5 thread.
Quick verdict
Both use a M20x1.5 thread.
- Thread size is the first hard-fit check for any comparison of spin-on filters.
- Gasket OD and gasket ID are the most important seal-related dimensions.
- Height differences can matter for clearance even when thread and gasket fit appear close.
- Bypass and anti-drainback differences may be important, depending on the application.
NAPA Gold 1381 and Baldwin B421 specifications
How matching is scored| Specification | NAPA Gold 1381 | Baldwin B421 |
|---|---|---|
| Thread size | M20x1.5 | M20x1.5 |
| Gasket OD | 63 mm | 64 mm |
| Gasket ID | 55 mm | 54.1 mm |
| Can OD | 92.99 mm | 76.2 mm |
| Height | 80 mm | 72.2 mm |
| Internal bypass valve | Yes | Yes |
| Bypass PSID | 12 - 15 | 14 |
| Anti-drainback valve | Yes | Yes |
What matters in this specific comparison
Thread size matches: both are M20x1.5.
Gasket OD differs by 1 mm (NAPA Gold 1381: 63 mm, Baldwin B421: 64 mm).
Gasket ID differs by 0.9 mm (NAPA Gold 1381: 55 mm, Baldwin B421: 54.1 mm).
NAPA Gold 1381 is 7.8 mm taller (NAPA Gold 1381: 80 mm, Baldwin B421: 72.2 mm) -- check clearance before substituting.
Can OD differs by 16.8 mm (NAPA Gold 1381: 92.99 mm, Baldwin B421: 76.2 mm).
Both open their bypass valve in a comparable range: NAPA Gold 1381 at 12-15 psi, Baldwin B421 at 14-14 psi.
Open related filters
Before substituting, verify thread fit, gasket sealing dimensions, height clearance, bypass behavior, and anti-drainback requirements for your specific application.