No UNF thread has 400 TPI — but if a drawing specified #0 UNF is 80 TPI max. 400 TPI would be specialty micro-threads for optics or fine adjustment screws.
Guide for identifying UNF threads:
Search your internal documentation or ask the manufacturer. Many custom parts have codes like WUNF-400 (e.g., WUNF = Westinghouse Unified National Fine?).
Even the best seal will fail if installed incorrectly. The WUNF 400, due to its hardness, is less forgiving than rubber. wunf 400
Do not use screwdrivers or metal picks. Use a nylon or brass seal pick.
Despite its robust design, users may encounter issues with the WUNF 400. Here is a quick troubleshooting guide:
Problem: The WUNF 400 nut feels "gritty" during threading.
Solution: Stop immediately. The nickel plating has likely flaked. Attempting to force the nut will cold-weld the threads (galling). Replace the nut. No UNF thread has 400 TPI — but
Problem: Loss of clamp load after 1,000 cycles.
Solution: Check the mating surface flatness. The WUNF 400 requires a surface finish of 3.2 µm Ra or better. Rough surfaces embed and relax over time.
Problem: Hydraulic leak in the WUNF 400 actuator.
Solution: Inspect the rod seal. The 400 kN force creates significant side loads if the rod is misaligned by more than 0.5 degrees. Realign the mounting brackets.
TPU is sensitive to ozone. If the WUNF 400 sits idle in a warehouse near electric motors (which generate ozone) for 2+ years, surface cracks will appear. Solution: Store seals in dark, sealed bags away from motors. Search your internal documentation or ask the manufacturer
Many engineers wonder if they can substitute a standard PTFE or rubber wiper for a WUNF 400. Here is the comparison table:
| Feature | Standard Rubber Wiper (NBR) | PTFE Wiper | WUNF 400 (TPU) | | :--- | :--- | :--- | :--- | | Hardness | 70-80 Shore A | 55-65 Shore D | 95 Shore A | | Abrasion Resistance | Fair | Poor (softens) | Excellent | | Low Temp Flexibility | Good | Poor (stiff) | Very Good | | Extrusion Resistance | Low | High | Very High | | Cost | Low | High | Medium | | Best Use Case | Clean indoor hydraulics | High temp / Chem aggressive | Dirty, abrasive outdoors |
Conclusion: If your cylinder rod looks dirty after a shift, you need a WUNF 400.
As Industry 4.0 pushes toward predictive maintenance, the WUNF 400 is evolving. New variants feature X-ray detectable additives (for food-grade hydraulics) and conductive TPU (to dissipate static electricity in fuel handling systems). However, the core value remains: an aggressive, durable, abrasive-resistant wiper that protects the heart of your hydraulic system.