Disc Blade Axle Sizes Explained — Square vs. Round, 1" to 1-1/2"

Every disc blade has a center hole — sometimes called the axle hole, axle bore, or arbor — that has to match the axle on your machine. Get this wrong and the blade either won't fit at all, or it fits loose enough to shift under load and destroy the blade or the bearings. This is the single most common mistake we see on returned blades: right diameter, wrong center hole.

Square vs. round axles — the split

Almost every North American tandem disc, offset disc, and disc-ripper built after 1970 uses a square axle. The blade has a square center hole that keys onto a square-cross-section axle bar. Advantages: no torque slip, no keyways to shear, cheap to manufacture. Downsides: the corners of a square hole concentrate stress, so a wallowed-out square-hole blade must be retired.

Round axles show up on coulters, planter row-cleaners, no-till drills, some vertical-tillage tools, and rolling harrows. Round blades are held to the axle either with a splined interface, a keyway, a set screw, or clamped between spacers with friction alone. Round-axle setups slip more easily but tolerate wear better.

The four square-axle sizes that cover 90% of the market

  • 1-1/8" square — small tandem discs, older 3-point implements, some John Deere 200-series
  • 1-1/4" square — the modal size across the industry. Case IH 3900/3950, most Krause 4900, most Sunflower, most Great Plains
  • 1-1/2" square — heavy offsets and no-till discs: Case IH 496, JD 610/620, Krause 8000, Wishek 862NT
  • 1-3/4" and 2" square — rare, on very large offsets and industrial (Rome TAWH, big Wishek units)

Round-axle sizes

  • 1" round — the modal coulter size. Yetter 2967, JD 2410 coulters, Great Plains Turbo-Chisel, Sunflower 4530/4610
  • 1-1/8" round — some heavier coulter setups and Unverferth rolling harrows
  • Splined round — planter row-cleaners, some vertical-tillage tools with driven axles

How to measure your axle before ordering blades

  1. Pull one blade off the machine (or take the tape measure right to the axle bar).
  2. Measure flat-to-flat on a square axle. Don't measure corner-to-corner — that reads about 40% larger and will send you to the wrong blade.
  3. For round axles, measure the diameter across the widest point. Include any keyway or flat if present.
  4. Confirm the hole in the blade matches. The hole should slip on with maybe 1/32" of side play — any more and the blade will hammer the axle corners.
Not sure it fits your machine? Text a photo of your old blade to 515-686-5575 — we'll cross-check the diameter, thickness, and axle-hole shape against our catalog before you order. Same-day ship on orders placed by 12pm CT.

What if my axle size isn't standard?

A handful of older European machines (Lemken, Amazone) and some odd-year Case IH built in the 1980s use non-standard axle sizes. If you measure something that doesn't match any of the sizes above, take a photo of the axle and the old blade side-by-side and text it to us — we can usually source a custom-punched blade in one of two ways: (1) order a slightly oversized square-hole blade and re-punch to your size, or (2) mount an adapter sleeve. Adapter sleeves are usually the wrong call because they add slop and speed up wear.

The three axle problems that will destroy new blades

  1. Worn axle corners (square). If the axle has rounded off the corners from years of use, a new blade won't have anywhere to key. Fix the axle first, or expect the new blade to wallow out in a season.
  2. Loose blade fit. More than about 1/32" of gap and the blade hammers under load. This shows up as a mushroomed center hole and a scarred axle. Retire the blade before it goes.
  3. Wrong torque on the gang bolt. The clamping force of the gang bolt (spool + spacers + blades + spool + nut) is what actually keeps the blades from turning independently. Torque per spec — usually 300-450 ft-lb for 1-1/2" gang bolts.

Common axle-blade combos in our catalog

Once you know your axle size, filter our catalog:

Frequently Asked Questions

How do I know if my disc harrow uses a 1-1/4" or 1-1/2" axle?
Pull one blade and measure flat-to-flat across the center hole with a caliper or a good tape measure. Don't measure corner-to-corner (that reads bigger than the flat-to-flat dimension). If the flat-to-flat is 1.24-1.26", you have a 1-1/4" square axle. If it's 1.49-1.51", you have 1-1/2".
Are coulter blades always round-axle?
Almost always, yes. The coulter cuts through residue but doesn't need to hold torque like a harrow gang blade, so a friction-clamped round axle is fine and simpler. Rare exceptions: heavy no-till coulter carts sometimes run square axles.
Can I use a square-hole blade on a round axle with a sleeve?
It works, but it introduces slop. The blade hammers the sleeve and the sleeve wallows out on the axle. If your axle is genuinely round, buy round-hole blades. If it's an old square that's worn nearly round, replace the axle before you replace the blades — new blades on a worn axle will fail fast.
What torque should I use on the disc gang bolt?
It depends on axle diameter and the manufacturer, but a rough working range: 1-1/4" square gang bolt = 250-350 ft-lb; 1-1/2" square gang bolt = 350-500 ft-lb. Consult your owner's manual for the exact spec — Krause, Case IH, and John Deere all publish it.
Are all 1-1/2" square axles the same?
Nominally, yes — but there's some tolerance variance between manufacturers. A blade punched for a Krause 1-1/2" axle will drop onto a Case IH 1-1/2" axle, but the fit may be slightly loose or tight. Order to fit the machine you have.