Description
How to measure a belt
The quickest way to find a replacement is the code printed on the back of your old belt. If it's worn off, a few simple measurements will usually tell us exactly what you need. You'll want a ruler or, better still, a pair of calipers, and a flexible tape measure.
Check for a code first
- V and wedge beltsCodes like A68 or SPZ1250 give the section and length. A68 is an A section belt with a 68 inch inside length. SPZ1250 is an SPZ section with a 1250mm datum length.
- Timing beltsCodes like 8M-1200-20 give the tooth pitch (8mm), the length (1200mm) and the width (20mm).
- Ribbed beltsCodes like 6PK1200 give the number of ribs (6), the section (PK) and the length (1200mm).
If you've got a code, search for it or send it to us. If not, follow the steps for your type of belt below.
V and wedge belts
- Measure the top width.Measure straight across the widest, flat top of the belt.
- Measure the depth.Measure from the top of the belt to the bottom. This is what tells classical and wedge belts apart.
- Check the underside.If it has notches cut into it, it's a cogged belt. Let us know, as cogged belts have an X in the code, such as AX or XPZ.
- Measure the length.See measuring length below.
| Section | Type | Top width | Depth |
|---|---|---|---|
| Z | Classical | 10mm | 6mm |
| A | Classical | 13mm | 8mm |
| B | Classical | 17mm | 11mm |
| C | Classical | 22mm | 14mm |
| D | Classical | 32mm | 19mm |
| SPZ | Wedge | 9.7mm | 8mm |
| SPA | Wedge | 12.7mm | 10mm |
| SPB | Wedge | 16.3mm | 13mm |
| SPC | Wedge | 22mm | 18mm |
Classical or wedge? Some sections are almost the same width. A Z and an SPZ are both about 10mm across, but the SPZ is deeper at 8mm, against 6mm for the Z. The depth is what gives it away.
Timing belts
- Measure the tooth pitch.This is the distance from the centre of one tooth to the centre of the next. It's the most important measurement on a timing belt.
- Count the teeth.Count every tooth round the belt. Mark your starting tooth with a pen so you don't lose count.
- Measure the width.Measure straight across the belt in millimetres.
- Note the tooth shape.Rounded teeth and trapezoid-shaped teeth can have the same pitch but won't fit the same pulleys. A photo side-on to the teeth helps us tell them apart.
Get an accurate pitch: measure from the centre of one tooth to the centre of the tooth ten along, then divide by ten. Small differences matter, as 5mm and 5.08mm pitch belts look almost identical. Once you have the pitch, multiply it by the number of teeth to get the belt's length.
| Pitch | Belt types |
|---|---|
| 2.032mm | MXL |
| 3mm | 3M, S3M |
| 5mm | 5M, S5M, T5, AT5 |
| 5.08mm | XL |
| 8mm | 8M, S8M |
| 9.525mm | L |
| 10mm | T10, AT10 |
| 12.7mm | H |
| 14mm | 14M, S14M |
| 22.225mm | XH |
Ribbed belts
- Measure the belt width.Measure straight across the back of the belt, from edge to edge.
- Count the ribs.Count the V-shaped ribs running along the underside.
- Work out the section.Divide the width by the number of ribs to get the rib pitch, then match it to the table below.
- Measure the length.See measuring length below.
| Section | Rib pitch (width ÷ ribs) | Typical use |
|---|---|---|
| PH | 1.60mm | Small appliances and light drives |
| PJ | 2.34mm | Power tools, appliances, fitness equipment |
| PK | 3.56mm | Vehicles, machinery and garden equipment |
| PL | 4.70mm | Heavier industrial drives |
| PM | 9.40mm | Heavy-duty industrial drives |
Example: a belt 21.4mm wide with 6 ribs has a rib pitch of 21.4 ÷ 6 = 3.56mm. That's a PK section, so the belt is a 6PK. Send us the width and rib count and we'll do the maths for you.
Measuring length
- Round the beltWrap a flexible tape measure round the outside of the belt and note the reading. Tell us it's an outside measurement.
- Round the pulleysIf the belt has snapped or gone missing, run a tape measure round the pulleys on the machine, following the path the belt takes, with the tensioner in its normal running position.
- Count the teethFor timing belts, tooth count multiplied by pitch gives the length. It's more accurate than measuring with a tape.
Old belts stretch and wear, so a measurement from a worn belt can be a little out. Tell us if the belt was badly worn or loose, and we'll take that into account.
Send us your measurements
Email your measurements with a photo of the belt, or give us a call. We'll work out what fits.
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