A BX77 is a cogged B-section V-belt: 17 mm wide, 77 inches inside and 80 inches outside, on the same pulleys as a B77. The X means cogged, so an AX or BX belt keeps the top width, pulleys and length number of its A or B twin. We sell it as the BX77 cogged V-belt.
XPZ is the cogged version of SPZ in the same way. If you already know your number, you can stop here. The table has the three pairs side by side.
| A | AX | B | BX | SPZ | XPZ | |
|---|---|---|---|---|---|---|
| Build | Plain, wrapped | Cogged | Plain, wrapped | Cogged | Plain, wrapped | Cogged |
| Top width | 13 mm (1/2") | 13 mm | 17 mm | 17 mm | 10 mm | 10 mm |
| Height | 8 mm | 8 mm | 11 mm | 11 mm | 8 mm | 8 mm |
| The number is | Inside length, inches | Inside length, inches | Inside length, inches | Inside length, inches | Datum length, mm | Datum length, mm |
| Outside length | Number + 2" | Number + 2" | Number + 3" | Number + 3" | No inch offset: go by the number | No inch offset: go by the number |
| Runs on | A pulleys | A pulleys | B pulleys | B pulleys | SPZ pulleys | SPZ pulleys |
| Smallest recommended pulley | 80 mm | 56 mm | 112 mm | 80 mm | 71 mm | 56 mm |
Source: belt makers' published section tables (see Sources); our product listings for n107, n112, n346 and n353. Read 30 September 2026.
The X changes how the belt is built, not its size
In a belt code, the X means cogged: moulded notch construction. Cogged, notched and toothed all mean the same thing here: notches moulded across the underside of the belt. Cogged AX and BX belts also have raw rubber sides with no fabric cover.
The size doesn't change. An AX93 and an A93 are both 2400 mm datum and 2415 mm outside, and a BX77 and a B77 are both 2005 mm datum and 2030 mm outside. AX belts run on standard A pulleys, BX belts on standard B pulleys and XPZ belts on standard SPZ pulleys.
So going from plain to cogged is usually the easy direction: buy the same number with an X. The exception is a drive that slips, clutches or runs in dirt. Belt makers recommend a wrapped belt there, and rate notched raw-edge belts for clean, guarded drives with little slip. Going back is where the pulley size matters. A cogged belt bends round a smaller pulley, and the recommended minimums for plain belts are much larger: 112 mm for a B against 80 mm for a BX. Below the minimum, belt makers warn, belt life is severely reduced. If the machine came with a cogged belt, measure the smallest pulley before fitting a plain one.
What an AX or BX number means
The letters give the section and the number gives the inside length in inches. Add 2 inches for the outside length of an AX, or 3 inches for a BX. Here are some of the sizes people search for most:
| Belt | Section | Inside | Outside | Outside (mm) | Plain twin |
|---|---|---|---|---|---|
| BX77 | B, cogged | 77" | 80" | 2030 | B77 |
| AX99 | A, cogged | 99" | 101" | 2565 (as A99) | A99 |
| BX49 | B, cogged | 49" | 52" | 1320 | B49 |
| BX99 | B, cogged | 99" | 102" | 2590 | B99 |
| BX65 | B, cogged | 65" | 68" | 1725 | B65 |
| AX88 | A, cogged | 88" | 90" | 2285 | A88 |
| AX70 | A, cogged | 70" | 72" | 1830 | A70 |
| BX42 | B, cogged | 42" | 45" | 1145 | B42 |
| AX35 | A, cogged | 35" | 37" | 940 | A35 |
Source: millimetres from belt makers' published section tables (see Sources; no AX99 is listed there, and the A99 is 2565 mm outside); inside and outside inches from our product listings (n107, n108, n112, n113, pn1180). Read 30 September 2026.
When is a cogged belt better?
Belt makers notch a belt for small pulleys and heat. The notches cut the bending stress as the belt wraps a small pulley, and so cut the heat from constant flexing, one cause of early belt failure.
Our AX listings give a working range of -25°C to +100°C. Cogged belts can also be rated wider on temperature than plain ones: in one belt maker's catalogue, its plain classical belts run from -35°C to +60°C and its cogged AX and BX from -57°C to +121°C, and it puts its cogged belts at 15% more capacity than its wrapped ones. Those figures are for that maker's belts, not ours.
SPZ vs XPZ: same pulley, same number
SPZ and XPZ are both 10 mm wide and 8 mm high, and both numbers are the datum length in millimetres. An XPZ1000 replaces an SPZ1000 on the same pulley. There's no inch offset to add, so go by the number on the old belt.
XPZ is rated down to a 56 mm pulley against 71 mm for SPZ. Belt makers' catalogues also list US 3VX equivalents for XPZ sizes, but warn not to mix XPZ and 3VX belts on the same drive. Our XPZ listing runs from XPZ630 to XPZ1600, and our SPZ listing from SPZ630 to SPZ3550.
How to tell which belt you have
- Read the code on the back of the old belt, or in the machine's manual. If it says AX, BX or XPZ, buy the same code. We'd go by the maker's belt number before a tape measure.
- No code? Measure the top width with a steel rule. 13 mm is A or AX. 17 mm is B or BX. 10 mm and about 8 mm deep is SPZ or XPZ. A 10 mm belt only 6 mm deep is a Z (also sold as M), which is a different belt.
- Look underneath. Notches across the underside mean cogged, so the code has an X. A smooth underside means a plain A, B or SPZ.
- Measure the outside length with a tape round the back of the belt. Take off 2 inches for A or AX, 3 inches for B or BX. For SPZ or XPZ, go by the number on the old belt. A tape measurement can land between two close sizes, so if the code has worn off, message us with the measurement.
- Swapping cogged for plain? Measure the outside diameter of the smallest pulley and check it against the minimum in the first table.
Which Bearings Express belt fits
- Pick the BX77 cogged V-belt if your old belt reads BX77 or B77.
- Pick the AX99 cogged V-belt if your old belt reads AX99 or A99.
- Pick the AX20 to AX59 range for shorter AX sizes, such as AX35 or AX42.
- Pick the BX24 to BX79 range for any other BX size in that span, such as BX49, BX65 or BX42.
- Pick the XPZ630 to XPZ1600 range for a cogged XPZ, or in place of an SPZ on the same pulleys.
- Pick the SPZ630 to SPZ3550 range for a plain SPZ, or for SPZ lengths past XPZ1600.
Every BX size we carry, BX24 to BX100, is in the BX-section V-belt collection.
Questions people also ask
What is the difference between AX and A belts?
The build. An AX has notches moulded into its underside and raw sides; an A is smooth and fabric-wrapped. Both are 13 mm wide, run on A pulleys and share the same size number, but the AX takes smaller pulleys and a wrapped A copes better with slip and dirt.
Can I use a BX belt instead of a B belt?
Yes, on the same B pulleys: a B77 becomes a BX77. The exception is a drive that slips or runs in dirt, where belt makers recommend a wrapped B belt. The reverse swap needs a check: the smallest recommended pulley for a plain B belt is 112 mm.
Are cogged belts better?
On small pulleys and hot, clean drives, yes. Cogged belts are rated for smaller pulleys and higher temperatures than plain ones. On a drive that slips, clutches or runs in dirt and debris, belt makers recommend a wrapped (plain) belt instead.
Is a Browning BX65 the same as a BX65?
BX65 is a standard size code (an RMA size reference), not one maker's part number, and Browning uses the same BX65 code. A BX65 is 65 inches inside and 68 inches outside (1725 mm).
What size is an SPZ1000 belt?
It's 10 mm wide with a 1000 mm datum length. An XPZ1000 is the same size in the cogged build.
Related reading
- Mower belt listed as "1/2 x 95"? How to turn it into an A or AK belt size
- V-belt sizes chart: A, B, C, Z (M) and SPZ widths, and how to read the number
- Do I need a Kevlar mower belt?
Sources
- Gates Australia, Industrial Power Transmission South Pacific Catalogue (2018): features guide on notched V-belts (PDF p. 6); Hi-Power II sections p. 29, A and B length tables pp. 31 and 33, pulley notes pp. 32 and 34; Tri-Power sections and advantages p. 45, AX table p. 46, BX table pp. 47 and 48; Super HC p. 51 and SPZ table p. 52; Quad-Power 4 p. 61 and XPZ table p. 62; minimum recommended pulley diameters p. 175; belt operating temperatures p. 176. Read 30 September 2026.
- Gates, Belt I.D. Chart (12998-J). Read 30 September 2026.
- Regal Rexnord (Browning), BX65 and B65 belt pages: https://www.regalrexnord.com/products/mechanical-power-transmission-components/belt-drives/belts/classical-belts/epdm-notched-belt-98-efficient-1089838 and https://www.regalrexnord.com/products/mechanical-power-transmission-components/belt-drives/belts/classical-belts/neoprene-wrapped-belt-95-efficient-1083203, page titles read 30 September 2026.
Checked against the belt makers' catalogues above and Bearings Express product data on 30 September 2026.
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