How to measure a V-belt pulley
Most pulleys have their size stamped on the face or the rim. If yours is worn, painted over or hidden behind a guard, five quick checks will tell us exactly what you need: the groove section, the diameter, the number of grooves and how it fixes to the shaft. A pair of calipers or a steel rule is all you need.
Check for a code first
- Taper lock pulleysA code like SPA 160-3-2012 gives the groove section (SPA), the pitch diameter (160mm), the number of grooves (3) and the taper bush it takes (2012).
- Pilot bore pulleysA code like SPB 200-2 PB gives the section, pitch diameter and grooves. PB means pilot bore: a plain hub you bore out to fit your shaft.
- Taper bushesThe bush has its own number stamped on the face, such as 2012, with the bore size, such as 35mm. Note both.
If you've got a code, search for it or send it to us. If not, follow the steps below.
Groove section
- Measure the groove top width.Measure straight across the top of one groove, where it meets the rim.
- Measure the groove spacing.On pulleys with two or more grooves, measure from the centre of one groove to the centre of the next. This doesn't change as the pulley wears, so it's the most reliable check.
- Match it to the table.The top width and spacing together tell you whether it's SPZ, SPA, SPB or SPC.
| Pulley | Groove top width | Groove spacing | Takes these belts |
|---|---|---|---|
| SPZ | 9.7mm | 12mm | SPZ, XPZ and Z (10mm) |
| SPA | 12.7mm | 15mm | SPA, XPA and A (13mm) |
| SPB | 16.3mm | 19mm | SPB, XPB and B (17mm) |
| SPC | 22mm | 25.5mm | SPC, XPC and C (22mm) |
Quickest check: lay one of your belts in the groove. A belt of the right section sits level with the rim or just above it. If it sinks well below the rim, the pulley is a size bigger or the groove is worn. If it sits high and only touches at the top, the pulley is a size smaller.
Diameter
- Measure the outside diameter.Measure straight across the pulley from rim to rim, through the centre, at its widest point.
- Work out the pitch diameter.Pulleys are sold by pitch diameter, which is where the belt runs, a little inside the rim. Take the figure for your section in the table below off the outside diameter.
- Round to the nearest standard size.Pitch diameters come in standard steps, such as 100, 106, 112, 118 and 125mm. Your answer should land on or very near one of them.
| Pulley | Take off the outside diameter | Example |
|---|---|---|
| SPZ | 4mm | 104mm outside = 100mm pitch, an SPZ 100 |
| SPA | 5.5mm | 165.5mm outside = 160mm pitch, an SPA 160 |
| SPB | 7mm | 207mm outside = 200mm pitch, an SPB 200 |
| SPC | 9.6mm | 259.6mm outside = 250mm pitch, an SPC 250 |
Measure through the centre. A tape laid across the face can easily miss the centre and read short. Calipers or a steel rule held against the rim on both sides give the most accurate reading. If the pulley is still on the machine, measure the rim at the top and bottom rather than across a guard.
Grooves and mounting
- Count the grooves.Count every groove on the pulley, even any your drive doesn't use. The replacement needs the same number to line up.
- Check how it fixes to the shaft.A taper lock pulley has a separate bush in the centre, held by two or three screws sitting in half-holes. A pilot bore pulley has a solid hub with a plain hole, usually with a grub screw and keyway.
- Taper lock: note the bush number and bore.Both are stamped on the face of the bush, for example 2012 and 35mm. If you can't read them, measure the shaft and the keyway width.
- Pilot bore: measure the bore and keyway.Measure the hole across its widest point, and the width of the keyway slot.
Taper lock bushes
The bush number tells you its size. The first two digits are roughly the outside diameter and the last two the length, both in tenths of an inch, so a 2517 is about 2.5 inches across and 1.75 inches long. Each bush size comes in a range of bores, so you need the bush number and the bore.
| Bush | Metric bores available |
|---|---|
| 1008 | 10mm to 25mm |
| 1108 | 10mm to 28mm |
| 1210 | 11mm to 32mm |
| 1610 | 14mm to 42mm |
| 1615 | 14mm to 42mm |
| 2012 | 14mm to 50mm |
| 2517 | 16mm to 65mm |
| 3020 | 25mm to 75mm |
| 3525 | 35mm to 90mm |
Check the grooves while you're there. If the groove walls are dished or polished, or the belt rides low in the groove, the pulley is worn. A worn pulley wears out new belts quickly, so it's worth replacing the pulley and belts together.
Find your pulley
Send us your measurements
Email your measurements with a photo of the pulley face, or give us a call. We'll work out what fits.