for Spartan Lawn Mower Blade Bolt & Lock Washer 418-0078-00 419-0004-00

What It Is

This is the OEM blade bolt and lock washer set (part numbers 418-0078-00 and 419-0004-00) for Spartan zero-turn mowers. It secures the mower blade to the spindle, preventing the blade from loosening during operation.

Fitment & Compatibility

Before buying, confirm your Spartan model uses a 5/16"-24 thread bolt (standard for most RT, RZ, and S series decks). Measure your existing bolt length—this bolt is approximately 1.25 inches long. Check your deck size: it fits 48", 52", and 60" Spartan decks, but not older 42" models. This is an OEM Spartan part, so it matches factory specs exactly. If you have a third-party blade or spindle, verify the bolt hole is not stripped or oversized.

Key Things to Know

• Grade 8 quality – This bolt is heat-treated and stronger than standard hardware. Do not substitute with a lower-grade bolt from a hardware store; it can shear under load.
• Lock washer included – The 419-0004-00 lock washer is pre-installed on the bolt. Do not add a second washer, as it can prevent proper torque.
• Installation torque – Tighten to 35–45 ft-lbs. Over-tightening can strip the spindle threads; under-tightening can cause the blade to come loose.
• Common gotcha – The bolt head is 5/8" (metric 16mm). Use a socket, not a wrench, to avoid rounding the edges.

Should You Buy It

If you own a Spartan zero-turn and need a direct OEM replacement for a lost or worn blade bolt, this is the right choice. It’s a simple, one-and-done fix that matches factory specs. Skip it if you have a different brand or a non-Spartan deck—you’ll need a different thread pattern.