Husqvarna 578931503 Fuel Cap With Retainer

What It Is

The Husqvarna 578931503 Fuel Cap With Retainer is a genuine OEM replacement cap designed to seal the fuel tank on select Husqvarna walk-behind mowers and zero-turn riders. The integrated retainer (tether) prevents loss when refueling.

Fitment & Compatibility

Before buying, confirm your machine uses a bayonet-style (twist-lock) fuel neck, not a screw-on cap. This cap fits Husqvarna models with part number 578931503 in the original equipment list—primarily LC 221A, LC 221AR, LC 321A, LC 321AR, LC 421A, LC 421AR, LC 421AWD, LC 421AWDAR walk-behinds and Z242F, Z254F, Z421F zero-turn mowers. Also compatible with some Poulan Pro, Jonsered, and McCulloch models using the same fuel tank assembly. Measure your fuel neck outer diameter—this cap fits necks approximately 1.18 in (30 mm). Do not assume it fits all Husqvarna caps; cross-check your owner’s manual or existing cap part number.

Key Things to Know

• OEM quality – Made by Husqvarna, not an aftermarket knockoff. Expect consistent sealing and proper venting.
• Easy install – No tools required. Just twist off old cap, twist on new one, and clip the retainer to the fuel tank bracket or handle.
• Venting check – If your tank vents through the cap, ensure the new cap has a vent hole (most do). A non-venting cap can cause engine starvation.
• Common gotcha – The retainer tether is short (about 6 in). It will not reach far if your tank is mounted low or far from the handle—test before cutting the old one off.

Should You Buy It

If you own a compatible Husqvarna mower and your original cap is cracked, lost, or leaks, this is a direct, hassle-free replacement at a fair price. It’s not universal, so verify fitment first, but for the right machine it’s a solid, reliable fix.