A Kevlar mower belt beats a standard V-belt on almost every mower deck: in our experience, 99% of deck belts are Kevlar, and aramid cord handles heavier shock loads and stretches less than standard polyester cord. A Kevlar belt such as our A103K (AK103) can replace a standard belt of the same size, but not the other way round.
If your old belt had a K in its code, buy the K version of the same size and you can stop here.
| Standard V-belt | Kevlar (aramid) V-belt | |
|---|---|---|
| Tensile cord inside the belt | Usually polyester | Kevlar or other aramid |
| Shock loads | Lower | Heavier |
| Stretch over time | More, so more re-tensioning | Less |
| Mower deck (cutter) belts | Only very old mowers, such as early Victas | About 99% of the deck belts we sell |
| Can it replace the other type? | No. In a Kevlar position it can shred within hours | Yes, if it's the same size |
| Code on our belts | A103, B100 | AK103 (also written A103K), BK100 |
| Price | Cheaper | Dearer |
Source: the Bearings Express team (30 September 2026); our product listings, read 30 September 2026; belt makers' published data on aramid cord (see Sources), read 27 and 30 September 2026.
Match the old belt: Kevlar replaces standard, never the reverse
Our advice to customers is simple. If the old belt was Kevlar, buy Kevlar. A Kevlar belt can also replace a standard belt of the same size, but a standard belt can't replace a Kevlar one.
The reason is how hard a mower works a belt. A deck belt, also called a cutter belt, gets a jolt every time you engage the blades, and on some decks it bends backwards around an idler. Belt makers' catalogues rate aramid-corded belts for high-power, clutching, heavy shock-loaded and back-idler-driven lawn and garden equipment. Put a standard belt in that job and, in our team's words, it can "shred within hours".
That's why almost every deck belt we sell is Kevlar. The mowers that get away with a standard deck belt are very old ones, such as early Victas, designed before Kevlar belts existed. Even those get much more wear out of a Kevlar belt.
A back idler on its own doesn't settle it, though. At least one belt maker also rates a light-duty standard belt for back idler drives, and even lists it for lawn mowers. The old belt and its position on the mower are the better guide.
Do drive belts need Kevlar too?
Some do. Many drive belts (also called primary, transmission or clutch-to-cutter belts) need Kevlar as well. Plenty of primary belts can run a standard belt, but if the drive calls for Kevlar, a standard belt won't last. Again, match the old one.
What do A103K and AK103 mean?
They're the same belt, written two ways:
- A is the section: 13 mm (1/2") top width.
- 103 is the inside length in inches. An A belt is 2 inches longer outside, so an A103K is 105 inches outside.
- K means it's made with Kevlar.
Where the K goes depends on the supplier. Our supplier writes AK103, others write A103K, and our product titles show both so either search finds it. The same goes for B-section belts: BK100 and B100K are one belt.
How to choose the right Kevlar belt
- Read the old belt. A K in the code, or the words Kevlar, aramid or power rated, means a Kevlar-type belt. Colour isn't a safe test, so go by the code or the printing.
- Note where it runs. A deck or cutter belt is almost always Kevlar. For a drive belt, go by the old belt or the mower's manual.
- Can't tell? Fit Kevlar. It does both jobs, so it's the safe pick for an unknown belt of the right size.
- Get the size. Use the maker's belt number where you can. If you only have an outside length, take 2 inches off for an A belt or 3 inches for a B belt to get the number.
- Between two sizes? Aftermarket belts come in 1 inch steps. If the mower has little adjustment at the tight end, choose the larger belt. If it has little adjustment at the loose end, choose the smaller one.
- Order the K version of that size, for example AK103 for an A103 position.
Which Bearings Express Kevlar belt fits
- Pick the A103K Kevlar V-belt (AK103) if your old belt reads A103K or AK103 (103 inches inside, 105 outside).
- Pick the A80K to A158K / AK80 to AK158 Kevlar range for an A-section Kevlar belt from AK80 to AK158. It lists 46 sizes (every inch from AK80 to AK107, then selected longer sizes), so check yours is on the list.
- Pick the B-section Kevlar range, BK29 to BK88 for a shorter B belt, 17 mm wide.
- Pick the B-section Kevlar range, BK94 to BK162 for a longer B belt.
- Pick the Hustler 782292 / Toro 133-7075 Kevlar belt for the cutter deck on the Hustler 60 inch FasTrak and Super Duty, or the Toro TimeCutter HD and HD MyRide 48 inch models it lists.
- Pick the Greenfield GT18005 / GT02365 Kevlar belt for the Greenfield Evolution 32 and 34 inch cutter decks it lists. We also sell this number as a standard B100, but the Kevlar version replaces either one.
Mower belts by brand and position are in our mower belts collection.
Questions people also ask
Is aramid the same as Kevlar?
Yes, for buying a belt. Kevlar is a brand of para-aramid fibre, and belt makers describe these belts as made with Kevlar or aramid tensile cords. Belts sold as aramid, Kevlar or power rated are the same class of belt.
Kevlar vs rubber mower belt: what's the difference?
A Kevlar belt is still a rubber V-belt. The difference is the cord moulded inside it: standard belts usually use polyester cord, Kevlar belts use aramid cord.
Do Kevlar mower belts last longer?
In a mower they generally do. Our team finds even old mowers built for standard belts get more wear from Kevlar, and aramid cords give longer life under frequent shock loads and stretch less over time.
Can I put a standard belt on my mower deck for now?
We wouldn't. On a deck that calls for Kevlar, a standard belt can shred within hours. Fit the Kevlar version of the same size.
What Kevlar belt sizes are there?
We list A-section Kevlar belts from AK29 to AK158 (13 mm wide) and B-section from BK29 to BK162 (17 mm wide). AK80 upwards is in the range linked above, and AK29 to AK79 are in our shorter A-section Kevlar range in the A-section collection. Not every inch is stocked, so check your size is on the list.
Is there a Kevlar timing, serpentine or CVT belt?
Aramid cord isn't only used in V-belts: one belt maker's industrial catalogue offers it made to order on timing belts, for example. Those are different belt types bought by the machine's or vehicle's part number, and the Kevlar belts we list are V-belts.
Related reading
- Mower belt buyer's guide
- Mower belt listed as "1/2 x 95"? How to turn it into an A or AK belt size
- John Deere GX20072 / GY20570 belt: size and the Australian replacement
Sources
- Gates Australia, Industrial Power Transmission South Pacific Catalogue (2018): aramid cords (PDF p. 7), A and B section widths (printed p. 29), BladeRunner lawn and garden belts (printed p. 91), PoweRated and Truflex (printed p. 97), Synchro-Power (printed p. 141). Read 27 and 30 September 2026.
- Gates, Belt I.D. Chart (12998-J). Read 27 and 30 September 2026.
- Arclin, "What is Kevlar?" (reached from dupont.com/what-is-kevlar.html). https://www.arclin.com/kevlar/what-is-kevlar/, read 30 September 2026.
Checked against the Bearings Express team's own advice, the catalogues above and our product data on 30 September 2026.
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