Mower Blade Bolt Cross Reference: Grade 8 Chart (2026)

Thank you for reading this post, don't forget to subscribe!

⚡ Quick Answer:

Most mower blade bolts are 5/8″-11, 1/2″-13, or metric M12x1.25 depending on brand. Kubota uses M12x1.25 metric. John Deere uses 5/8″-11 or 1/2″-13. Exmark/Toro use 5/8″-11. Scag uses 5/8″-11 x 9-1/2″. Bad Boy uses 5/8″-18 fine thread. Husqvarna uses 7/16″-14. Always use minimum Grade 5 — Grade 8 or metric 10.9 is strongly recommended on commercial decks. Torque: 45–55 ft-lb for 1/2″-13, 65–75 ft-lb for 5/8″-11 Grade 8. Never use Grade 2 or generic zinc-plated bolts. Aftermarket Grade 8 bolts run $1–2.50 each vs $3–8 OEM — saving 60–75% per bolt.

Paying $3–8 per bolt at the dealer counter gets old fast when you are swapping or sharpening blades several times a season. On a six-bolt commercial deck that adds up to $18–48 per blade service — just in hardware. Aftermarket Grade 8 bolts in the correct size cost $1–2.50 each from farm stores or Amazon, saving 60–75% per bolt. This guide covers exact bolt sizes, grades, and torque specs for Kubota, John Deere, Exmark, Scag, Toro, Cub Cadet, Husqvarna, and Bad Boy — plus OEM part numbers and confirmed aftermarket equivalents.

🔧 3 Specs to Match When Cross-Referencing Blade Bolts

Thread size and pitch — 5/8″-11, 1/2″-13, 7/16″-14 (SAE) or M10x1.25, M12x1.25 (metric). Metric and SAE are NOT interchangeable — cross-threading destroys spindles
Bolt grade — minimum Grade 5 (metric 8.8) for all applications. Grade 8 (metric 10.9) required for commercial decks and 5/8″ hardware. Identified by radial lines on head: 3 lines = Grade 5, 6 lines = Grade 8
Torque — under-torquing causes blade wobble and bolt fatigue; over-torquing stretches threads or cracks spindle flanges. Always finish with a torque wrench

⚠️ Never use Grade 2 or generic zinc-plated bolts for mower blades.

Minimum Grade 5 or metric 8.8 is required. Grade 8 or metric 10.9 is strongly recommended on high-speed or commercial decks to withstand impact loads and centrifugal forces at blade tip speeds around 18,000 feet per minute.

Mower Blade Bolt Size by Brand — Quick Reference

Brand	Thread Size	Grade	Torque	Notes
Kubota (ZD/ZG series)	M12x1.25 x 30mm	8.8 or 10.9	55–65 ft-lb	Metric — never substitute SAE
John Deere (large deck)	5/8″-11 x 1-1/4″	Grade 8	65–75 ft-lb	48–60″ decks and ZTrak
John Deere (residential)	1/2″-13 x 1-3/8″	Grade 5 or 8	45–55 ft-lb	Lawn tractors and walk-behinds
Exmark (commercial)	5/8″-11 x 1-1/2″	Grade 8	65–75 ft-lb	Shares with Toro commercial
Scag (Tiger Cat/Turf Tiger)	5/8″-11 x 9-1/2″	Grade 8	70–80 ft-lb	Long bolt through stacked blades
Toro (commercial)	5/8″-11 x 1-1/2″	Grade 8	65–75 ft-lb	Same as Exmark 125-2466
Cub Cadet / MTD	M8-1.25 x 55mm	10.9	25–30 ft-lb	Some models use 1/2″-13 SAE
Husqvarna (riding mower)	7/16″-14 x ~1″	Grade 5	35–45 ft-lb	Integrated washer head design
Bad Boy (commercial)	5/8″-18 x 1-1/2″	Grade 8	70–80 ft-lb	Fine thread — not interchangeable with 5/8″-11

Kubota Blade Bolt Cross-Reference

OEM Part #	Thread Size	Grade	Torque	Aftermarket Equivalent
K5651-34372	M12x1.25 x 30mm	8.8 or 10.9	55–65 ft-lb	M12-1.25×30 Class 10.9 JIS Flange Bolt 4-Pack
K5651-34370	M12x1.25 x 18–20mm	8.8	50–60 ft-lb	M12-1.25×30 Class 8.8 Hex Flange Bolt 2-Pack
01135-51030	M10x1.25 x 30mm	8.8	40–50 ft-lb	Metric Flange Bolt Assortment Kit — includes M10

John Deere Blade Bolt Cross-Reference

OEM Part #	Thread Size	Grade	Torque	Aftermarket Equivalent
M112090	5/8″-11 x 1-1/4″	Grade 8	65–75 ft-lb	Grade 8 Hex 5/8-11 x 1-1/2″ 10-Pack
M118809	1/2″-13 x 1-3/8″	Grade 5 or 8	45–55 ft-lb	Grade 8 Hex 1/2-13 x 1-1/2″ 25-Pack
GX22456	1/2″-13 x 1-1/4″	Grade 5	45–50 ft-lb	Grade 8 Hex 1/2-13 x 1-1/4″ 25-Pack

Exmark & Toro Blade Bolt Cross-Reference

Brand / OEM Part #	Thread Size	Grade	Torque	Aftermarket Equivalent
Exmark 125-2466	5/8″-11 x 1-1/2″	Grade 8	65–75 ft-lb	125-2466 Blade Bolt Kit 4-Pack
Toro 125-2466	5/8″-11 x 1-1/2″	Grade 8	65–75 ft-lb	Grade 8 Hex 5/8-11 x 1-1/2″ 10-Pack

Scag Blade Bolt Cross-Reference

OEM Part #	Thread Size	Grade	Torque	Aftermarket Equivalent
04001-41	5/8″-11 x 9-1/2″	Grade 8	70–80 ft-lb	04001-41 Blade Bolt & Nut Kit 3-Pack
791170 (kit)	5/8″-11 x 9-1/2″	Grade 8	70–80 ft-lb	04001-41 04020-09 Bolt & Nut Kit 3-Pack

Husqvarna, Bad Boy & Cub Cadet Blade Bolt Cross-Reference

Brand / OEM Part #	Thread Size	Grade	Torque	Aftermarket Equivalent
Husqvarna 532193003	7/16″-14 x ~1″	Grade 5	35–45 ft-lb	532193003 Replacement 3-Pack
Bad Boy 018-6020-00	5/8″-18 x 1-1/2″	Grade 8	70–80 ft-lb	018-6020-00 Grade 8 Blade Bolt 3-Pack
Cub Cadet 710-04933	M8-1.25 x 55mm	10.9	25–30 ft-lb	Metric Flange Bolt Kit — includes M8

Always verify thread size with a caliper before ordering — metric and SAE bolts look similar but are NOT interchangeable. Cross-threading a spindle requires expensive replacement.

🔩 Top Aftermarket Blade Bolts — Grade 8, Save 60–75% vs OEM:

OEM blade bolts cost $3–8 each. These Grade 8 equivalents run $1–2.50 each. Same strength, massive savings. Buy in 10- or 25-packs for the season.

Grade 8 Hex 5/8-11 x 1-1/2″ — 10-Pack (Exmark, Toro, JD M112090)

Yellow zinc Grade 8, 150,000 PSI — direct replacement for Exmark 125-2466, Toro, JD commercial decks (~$1.54/bolt)

View

Grade 8 Hex 1/2-13 x 1-1/2″ — 25-Pack (JD M118809, Residential)

Best bulk value for residential decks — 25-pack at ~$1.16/bolt. JD lawn tractors, walk-behinds, residential zero-turns

View

04001-41 Scag Blade Bolt & Nut Kit — 3-Pack

Direct replacement for Scag Tiger Cat, Turf Tiger, all 32″–72″ models. Long 5/8-11 x 9-1/2″ Grade 8 with hex nuts (~$6.33/set)

View

M12-1.25×30 Class 10.9 JIS Flange Bolt — 4-Pack (Kubota K5651-34372)

Direct replacement for Kubota ZD-series blade bolts. Class 10.9 metric flange design (~$4/bolt)

View

Bad Boy 018-6020-00 Grade 8 Blade Bolt — 3-Pack

5/8″-18 fine thread Grade 8 — Bad Boy ZT, CZT, MZ, Outlaw, Maverick 60″ decks (~$4.30/bolt)

View

As an Amazon Associate, TractorPartsCentral earns from qualifying purchases.

💰 OEM vs Aftermarket Cost Comparison

Source	Price Per Bolt	6-Bolt Deck Cost	Annual Savings
Dealer OEM	$3–$8	$18–$48	—
Aftermarket Grade 8	$1–$2.50	$6–$15	$12–$33/service

Installation Best Practices

Disconnect battery or spark plug wire. Block blade to prevent rotation. Remove old bolt and inspect for stretched shank, damaged threads, or impact deformation — replace any suspect bolt.

Clean spindle threads with wire brush. Inspect for cross-threading or galling. Apply small amount of anti-seize to threads only if you reduce torque by 10% to compensate for reduced friction.

Install blade with cutting edges oriented correctly. Seat against spindle ensuring any key tabs or drive lugs fully engage. Install bolt with specified washer orientation.

Torque in two stages — for example 30 ft-lb then 65 ft-lb on a 5/8″-11 Grade 8 bolt. Always finish with a calibrated torque wrench. Impact wrenches can exceed 100 ft-lb and strip threads or crack spindle flanges.

Check torque after the first mowing session. Consider blue Loctite 242 on high-vibration commercial machines to resist loosening. Recheck bolts after any hard impact with stumps or rocks.

Aftermarket Grade 8 blade bolts in the correct thread size provide identical or better safety than OEM hardware at 60–75% lower cost. Match thread size (5/8″-11, 1/2″-13, or metric M12x1.25), use minimum Grade 8 on commercial decks, and always torque with a calibrated wrench. Never use Grade 2 or generic zinc hardware on blade applications. For complete deck maintenance see our Mower Blade Cross-Reference Guide and Deck Belt Cross-Reference Chart. For more guides visit TractorPartsCentral.com.

? Frequently Asked Questions

What size bolt is on a lawn mower blade?

It depends on the brand. Kubota uses M12x1.25 metric. John Deere large decks use 5/8″-11, residential models use 1/2″-13. Exmark and Toro commercial use 5/8″-11. Scag uses 5/8″-11 x 9-1/2″. Bad Boy uses 5/8″-18 fine thread. Husqvarna uses 7/16″-14. Cub Cadet/MTD spindles often use M8-1.25. Measure the threaded diameter with a caliper and use a thread gauge to confirm pitch before ordering replacements.

Does Kubota use metric or standard bolts?

Kubota uses metric bolts throughout — blade bolts are M12x1.25 on ZD and ZG series decks. Never substitute SAE hardware in Kubota spindles. A 1/2″-20 SAE bolt will partially thread into an M12x1.25 spindle but quickly damages threads requiring expensive spindle replacement. Always match metric to metric — identify by the “M12 x 1.25” or similar marking stamped on the bolt head.

Are mower blade bolts reverse thread?

Most mower blade bolts are standard right-hand thread — turn clockwise to tighten. Some older walk-behind mowers and certain brands use left-hand (reverse) thread on one side to prevent loosening from blade rotation. Check your operator’s manual or look for “L” stamped on the bolt head indicating left-hand thread. When in doubt, try turning the bolt slowly before applying force — if it tightens going counterclockwise it’s reverse thread.

Can I use Grade 5 instead of Grade 8 for mower blades?

Grade 5 works for many residential decks originally spec’d with Grade 5 hardware — typically 1/2″-13 or 7/16″ bolts at 45–55 ft-lb. However commercial mowers like Bad Boy (5/8″-18 Grade 8), Scag (5/8″-11 Grade 8), and Exmark (5/8″-11 Grade 8) are designed around higher-strength fasteners. Downgrading to Grade 5 on commercial applications is not recommended — the lower tensile strength is insufficient for the shock loads at 18,000 ft/min blade tip speed.

What socket size do I need for mower blade bolts?

For 5/8″-11 Grade 8 bolts (Exmark, Scag, JD M112090) use a 15/16″ socket. For 1/2″-13 bolts (JD residential, Toro TimeCutter) use a 3/4″ socket. For Kubota M12x1.25 metric bolts use an 18mm or 19mm socket depending on the head size. For Husqvarna 7/16″ bolts use an 11/16″ socket. For Bad Boy 5/8″-18 use a 15/16″ socket. Always use a breaker bar for initial loosening — blade bolts are typically tight from service torque and rust.

How often should I replace mower blade bolts?

Inspect at every blade change and replace immediately after any hard impact with stumps, rocks, or metal objects. Replace if you see stretched shank, damaged threads, bent shaft, or heavy corrosion. Commercial operators often replace annually as cheap insurance — at $1–2.50 per aftermarket Grade 8 bolt it costs $6–15 for a six-bolt deck. Homeowners can run bolts multiple seasons if threads and shanks remain in good condition after inspection.

Related Mower Parts & Maintenance Guides

Lawn Mower Blade Cross-Reference Guide →

OEM blade part numbers and aftermarket equivalents for all major brands

Mower Deck Belt Cross-Reference Chart →

Save 30–50% on deck belts for Kubota, JD, Exmark, Scag and more

Mower Spindle Assembly Interchange Guide →

Spindle cross-reference and rebuild guide for major mower brands

Mower Oil Filter Cross-Reference →

Kawasaki, Kohler, Briggs and Kubota oil filter equivalents

Kubota Filter Cross-Reference Master Chart →

All Kubota filter part numbers — oil, fuel, air and hydraulic

Kubota Maintenance Schedule →

Complete service intervals for all BX, B, L and M series models

This article contains affiliate links. TractorPartsCentral.com is a participant in the Amazon Services LLC Associates Program. When you purchase through our links, we may earn a small commission at no additional cost to you.