Why PTO Clutch Bore Size Matters
The PTO clutch bore is the hole through the center of the clutch that slides over the engine crankshaft. If the bore size is wrong, the clutch will not fit correctly, even if the mower model, pulley size, and part number look close.
The two most common PTO clutch bore sizes are 1 inch and 1-1/8 inch. They are close enough to confuse buyers, but they are not interchangeable. A 1-inch bore clutch will not slide onto a 1-1/8 inch crankshaft. A 1-1/8 inch bore clutch on a 1-inch crankshaft can fit loose, wobble, damage bearings, damage the keyway, or fail under load.
Fitment rule: match the original clutch number first, then confirm the crankshaft bore before ordering.
1-Inch vs 1-1/8 Inch Bore: Quick Comparison
| Bore Size | Decimal Size | Common Written Forms | Fitment Meaning |
|---|---|---|---|
| 1 inch | 1.000" | 1", 1 inch, 1.000 bore | Fits engines with a 1-inch crankshaft PTO end |
| 1-1/8 inch | 1.125" | 1-1/8", 1.125", 1.125 inch bore | Fits engines with a 1-1/8 inch crankshaft PTO end |
Do not guess from photos. Many PTO clutches look nearly identical from the outside but use different bore sizes internally.
Common 1-Inch Bore PTO Clutch Paths
These are common examples of 1-inch bore PTO clutch replacement paths. Always verify the original clutch number, pulley diameter, rotation, connector, and anti-rotation setup before ordering.
| Product Path | Common Brands / Models | Key Notes | Product Link |
|---|---|---|---|
| 917-04526A / Warner 5219-94 | Cub Cadet, MTD, Troy-Bilt, Craftsman | 1" bore, 6" pulley, CCW rotation | 917-04526A PTO clutch replacement |
| 917-05209 / Warner 5219-177 | Cub Cadet XT1, XT2, RZT, ZT1, ZT2, Troy-Bilt Mustang XP | 1" bore, 6" pulley, CCW rotation, MTD-built mower path | 917-05209 PTO clutch replacement |
| 917-05001 / Warner 5219-25 | Cub Cadet GT1554, SLT1554, LGT1050, Troy-Bilt GT / GTX | 1" bore, 6" pulley, CCW rotation, heavy-duty 50" / 54" deck path | 917-05001 PTO clutch replacement |
| 132732 / 539132732 / Warner 5219-69 | Husqvarna, AYP, Dixon, Yazoo Kees | 1" bore, CCW rotation, multi-brand fitment path | 132732 PTO clutch replacement |
| TCA15092 / TCA15488 | John Deere 7H17, 7G18, 7H19 commercial walk-behind mowers | 1" bore, CCW rotation, John Deere commercial walk-behind path | TCA15092 PTO clutch replacement |
| GDA10017 / Warner 5219-4 | John Deere, Great Dane, EverRide, Lesco, Landoll | 1" bore, 6" pulley, CCW rotation, pigtail lead path | GDA10017 PTO clutch replacement |
| AM141978 / Warner 5219-126 | John Deere Z625, Z645, Z655 Eztrak | 1" bore, CCW rotation, John Deere Eztrak path | AM141978 PTO clutch replacement |
| 00191700 / Warner 5219-45 | Ariens, Gravely | 1" bore, Ariens / Gravely replacement path | 00191700 PTO clutch replacement |
Common 1-1/8 Inch Bore PTO Clutch Paths
These are common examples of 1-1/8 inch bore PTO clutch replacement paths. A 1-1/8 inch bore is also written as 1.125".
| Product Path | Common Brands / Models | Key Notes | Product Link |
|---|---|---|---|
| 2722016 / Warner 5219-14 | Bobcat, Bunton, Woods, Case, Jacobsen, Ransomes | 1-1/8" bore, 6-5/16" pulley, CW rotation | 2722016 PTO clutch replacement |
| TCA12522 | John Deere 737, 757, 777, 797, M653, M655, M665 | 1-1/8" bore, John Deere commercial ZTrak path | TCA12522 PTO clutch replacement |
| TCA23182 | John Deere Quik-Trak 648R, 652B, 652R, 661R | 1-1/8" bore, commercial Quik-Trak path | TCA23182 PTO clutch replacement |
| AM131779 | John Deere 335, 345, GX335, GX345, GX355 early serial path | 1-1/8" bore, CCW rotation, verify serial and original clutch number | AM131779 PTO clutch replacement |
Important: these tables are routing examples, not a universal fitment list. The correct replacement still depends on the original part number, bore, pulley diameter, rotation, connector, and anti-rotation setup.
How to Measure PTO Clutch Bore Size
- Turn off the mower, remove the key, and let the engine cool completely.
- Disconnect the battery before working near the PTO clutch or wiring.
- Remove the deck belt from the PTO clutch pulley.
- Locate the center bore of the old clutch or measure the engine crankshaft PTO end.
- Use digital calipers if available. A tape measure is often too rough for this job.
- A 1-inch crankshaft should measure close to 1.000".
- A 1-1/8 inch crankshaft should measure close to 1.125".
If the old clutch is still installed and will not slide off the crankshaft, do not pry against the pulley or hammer on the clutch. Read the PTO clutch stuck on crankshaft guide before removal causes crankshaft, keyway, or bearing damage.
What Happens If the PTO Clutch Bore Is Wrong?
If the bore is too small
A clutch with a bore that is too small will not slide onto the crankshaft. For example, a 1-inch bore clutch will not fit a 1-1/8 inch crankshaft. Forcing it can damage the clutch bearing, crankshaft surface, or keyway.
If the bore is too large
A clutch with a bore that is too large may slide on, but it can run loose. That can cause wobble, vibration, bearing damage, keyway damage, belt misalignment, pulley wear, or clutch failure.
If the bore is close but not exact
Close is not good enough. PTO clutches operate under sudden blade engagement loads. The bore must match the crankshaft correctly so the clutch runs centered and transfers torque safely.
Bore Size Is Only One Fitment Check
Even if the bore size is correct, the clutch can still be wrong. Before ordering, confirm all of these:
- Original part number: OEM, Warner, Xtreme, Ogura, or other number on the old clutch
- Crankshaft bore: 1", 1-1/8", or another confirmed size
- Pulley diameter: Match the pulley size and belt groove profile
- Rotation: CW or CCW from the pulley side
- Belt width: 1/2", 5/8", or A/B belt compatibility
- Connector style: Integral plug, pigtail lead, or matching harness
- Anti-rotation setup: Bracket, slot, or stop pin alignment
- Deck and serial range: Some mowers split by deck size, engine, or serial number
Need help with rotation? Read the PTO clutch rotation guide.
Why Model Number Alone Can Be Risky
Many mower models were built across multiple years, deck sizes, engine options, and supplier changes. A model name can point you in the right direction, but the original clutch number and physical specs should make the final decision.
For example, some John Deere, Toro, Cub Cadet, Husqvarna, and commercial mower applications have similar-looking PTO clutches with different bore sizes, pulley diameters, or rotation directions. Choosing by model alone can lead to a clutch that looks close but will not install correctly.
Related Fitment Guides
- Warner 5219 PTO clutch cross-reference guide
- PTO clutch rotation guide: CW vs CCW
- Fitment Guarantee
- PTO clutch installation guide
- PTO clutch won’t engage troubleshooting guide
- Full electric PTO clutch catalog
FAQ
Is a 1-inch PTO clutch bore the same as 1-1/8 inch?
No. A 1-inch bore is 1.000". A 1-1/8 inch bore is 1.125". They are different sizes and should not be treated as interchangeable.
Can I install a 1-inch bore clutch on a 1-1/8 inch crankshaft?
No. A 1-inch bore clutch will not properly fit a 1-1/8 inch crankshaft. Forcing it can damage the clutch, crankshaft, bearing, or keyway.
Can I install a 1-1/8 inch bore clutch on a 1-inch crankshaft?
No. A 1-1/8 inch bore clutch can be loose on a 1-inch crankshaft. That can cause wobble, vibration, belt misalignment, and clutch failure.
How do I know what bore size my PTO clutch uses?
Check the original clutch number first. Then confirm the bore by measuring the crankshaft PTO end or the old clutch bore with calipers. Many listings also show the bore size in the product specs.
Is bore size enough to confirm PTO clutch fitment?
No. Bore size is only one fitment check. You also need to confirm pulley diameter, rotation, belt width, connector style, anti-rotation setup, mower model, serial range, and original part number.
Why does my new PTO clutch slide on but wobble?
A wobbling clutch can be caused by the wrong bore size, worn crankshaft, damaged keyway, missing hardware, incorrect spacer, or improper installation. Stop using the mower until the fitment and installation are checked.
Can PTO Direct USA help confirm bore size before I order?
Yes. Email support@ptodirectusa.com with your mower model number, serial number, deck size, original clutch number, and clear photos of the old clutch. Include photos of the clutch label, center bore, pulley, connector, anti-rotation bracket, and crankshaft area.