Guide · Blade bolts, adapters and deck wheels
Mower blade adapters: bore, height and pulley
A walk-behind blade adapter is identified by its bore, its height and whether it has a pulley. Troy-Bilt's numbers, and why the blade hole must match it.
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Short answer
A blade adapter is identified by its inside diameter (bore), its height and whether it has a pulley. Troy-Bilt sells adapters with the same 7/8-inch or 25 mm bore in different heights, including versions with a pulley.[1] The bore alone does not identify an adapter, so order by the part number in your mower's parts list.
What an adapter does
On many walk-behind mowers, the adapter sits between the engine or motor shaft and the blade. Its bore slides onto the shaft, and its lower face carries a shape that locates the blade's center hole. Some adapters also carry the pulley that drives the self-propel belt. Get any of the three properties wrong and the blade will not seat as the maker designed.
Bore: 7/8 inch and 25 mm
Troy-Bilt sells walk-behind blade adapters in both 7/8-inch and 25 mm inside diameters.[1] Its listing shows 748-0376E and 490-950-F090 at 7/8 inch and 748-04096 at 25 mm.[1] The two are close in size but they are separate parts. Do not treat them as interchangeable.
Height
Troy-Bilt sells adapters with the same 7/8-inch bore in different heights.[1] Its product names give two figures: 748-0376E is named "1.19 in x 7/8 in Inside Dia." and 748-0377E "2.15 in x 7/8 in Inside Dia."[1] Troy-Bilt's site filters adapters by height, but the names themselves do not label the first figure, so read it as the part's name, not a drawing dimension. A taller or shorter adapter changes where the blade sits under the deck.
Pulley
Some Troy-Bilt blade adapters come with an integrated pulley, such as 687-02539, listed as "Blade Adapter w/ Pulley - 2.85 in x 7/8 in Inside Dia."[1] Troy-Bilt also lists 687-02528 and 687-02220 among its pulley adapters.[1] If your old adapter has a pulley, the replacement needs one too.
| Adapter (Troy-Bilt) | Bore | Height (as named) | Pulley |
|---|---|---|---|
| 748-0376E | 7/8 in | 1.19 in | Not in the name |
| 748-0377E | 7/8 in | 2.15 in | Not in the name |
| 687-02539 | 7/8 in | 2.85 in | Yes, "w/ Pulley" |
| 748-04096 | 25 mm | Not given here | Not given here |
Source for all rows: Troy-Bilt's blade adapter listing.[1]
Toro Recyclers are another case. Stens lists its 400-320 adapter for Toro Recyclers from 2002 on, with a 1-inch crank diameter, replacing Toro 104-8687, 104-8695 and 106-3987, and says the OEM washer and spacer must be used.[2]
Picks that fit1 product
Choose the Stens 400-320 only if your Toro Recycler's parts list shows 104-8687, 104-8695 or 106-3987; newer Recyclers list other blade drivers.
More on choosing
Reuse the OEM washer and spacer, as Stens says. On Amazon, check that Ships from / Sold by is Amazon.com or Stens.
Blade adapter for 2002-and-later Toro Recyclers
Stens 400‑320 blade adapter for Toro Recycler mowers (2002 and newer), 1 in crank
The blade side: hole shapes must match
The blade's center hole has to match the adapter or spindle it mounts on. Oregon explains two cases for MTD-built mowers:
- MTD-built walk-behind blades with a bow-tie hole are replaced by Oregon blades with a rectangular center hole that fits the bow-tie pattern on the blade adapter.[3] See the bow-tie center hole page.
- MTD-built blades with a 6-point star are replaced by Oregon blades with a Y-shaped center hole that fits the 6-point star on the spindle.[3] See the 6-point star page.
Those are Oregon's stated fits for MTD-built parts. Do not extend them to other brands. Troy-Bilt's site filters adapters by patterns such as bow tie and round, but does not give a pattern for each part number,[1] so check the shape on your old adapter. The round center hole page and the center hole shapes guide cover the others.
Why "make it fit" is the wrong answer
Adapters and spindles carry the blade's load at full speed. When those parts fail, they can be recalled: in January 2018, SureFit recalled riding-mower blade spindle shafts and assemblies, models 504-00341 and 504-00346, sold as aftermarket replacements for John Deere riding mowers, because the shaft can break and eject pieces.[4] That recall is about those two parts only, but it shows what is at stake. A blade that needs a ground-out hole or a re-cut keyway is the wrong blade.
Next
Questions
What size blade adapter do I need?
The part number your mower's parts list shows. Troy-Bilt sells adapters with the same bore in different heights, some with a pulley, so the bore alone does not identify one.[1]
Are 7/8 in and 25 mm adapters the same?
No. Troy-Bilt sells walk-behind blade adapters in both 7/8-inch and 25 mm inside diameters as separate parts; do not treat them as interchangeable.[1]
Does the adapter's hole shape matter?
Yes. The blade's center hole must match the adapter or spindle. Oregon, for example, says its rectangular-hole blades fit the bow-tie pattern on MTD-built blade adapters.[3]
Can I fit a different blade by changing the adapter?
Only with an adapter and blade your mower's maker lists together. Never grind, drill or alter an adapter, spindle or blade to make parts fit.