Free help & advice Learn more

How to Measure a Part

How to measure a part

The quickest way to find a replacement is the part number stamped or printed on the old one. If it's worn off, a few simple measurements will usually tell us exactly what you need. For most parts you'll want a pair of calipers, and for belts a flexible tape measure too.

Check for a part number first

  • BearingsNumbers like 6205-2RS give the type, size and seals. The last two digits of the main number usually give the bore.
  • Oil sealsSizes like 30x47x7 give the shaft diameter, housing bore and width in millimetres.
  • Belts and chainCodes like SPB1250, 8M-1200-20 or 08B-1 give the section or pitch, and often the length.

If you've got a number, search for it or send it to us. If not, follow the steps for your part below.

Bearings

  1. Measure the bore.Measure the inside diameter, where the shaft goes through.
  2. Measure the outside diameter.Measure straight across the outer ring at its widest point.
  3. Measure the width.Measure the thickness of the bearing from one face to the other.
  4. Check the sides.Rubber seals (2RS), metal shields (ZZ) or open? Note any letters stamped on the face, too.
Outside diameter Bore Width side view
Measure the bore, outside diameter and width.
Reading the bore from a bearing number
Last two digits Bore
00 10mm
01 12mm
02 15mm
03 17mm
04 and above Multiply by 5 (05 = 25mm, 10 = 50mm)

Measure the shaft if you can. An old bearing can be worn or damaged, so the shaft and housing it fits are a more reliable guide. Measurements are usually whole millimetres, or exact fractions of an inch on imperial bearings.

Oil seals

  1. Measure the shaft.Measure the diameter of the shaft the seal runs on. Don't measure the old seal's inner lip, which stretches in use.
  2. Measure the housing bore.Measure the diameter of the hole the seal sits in, or the outside of the old seal.
  3. Measure the width.Measure the thickness of the seal.
  4. Note the material and style.Standard seals are nitrile. Brown seals are usually Viton, for high temperatures. Note if it has a second dust lip.
Housing bore Shaft Width side view
Seals are sized shaft x housing x width, such as 30x47x7.

V and wedge belts

  1. Measure the top width.Measure straight across the widest, flat top of the belt.
  2. Measure the depth.Measure from the top of the belt to the bottom. This is what tells classical and wedge belts apart.
  3. Check the underside.If it has notches cut into it, it's a cogged belt, which has an X in the code, such as AX or XPZ.
  4. Measure the length.Wrap a flexible tape measure round the outside of the belt, or run it round the pulleys on the machine.
Top width Depth
Measure the top width and the depth.
V and wedge belt sizes
Section Type Top width Depth
Z Classical 10mm 6mm
A Classical 13mm 8mm
B Classical 17mm 11mm
C Classical 22mm 14mm
SPZ Wedge 9.7mm 8mm
SPA Wedge 12.7mm 10mm
SPB Wedge 16.3mm 13mm
SPC Wedge 22mm 18mm

Classical or wedge? A Z and an SPZ are both about 10mm across, but the SPZ is deeper at 8mm, against 6mm for the Z. The depth gives it away.

Timing belts

  1. 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.
  2. Count the teeth.Count every tooth round the belt. Mark your starting tooth with a pen so you don't lose count.
  3. Measure the width.Measure straight across the belt in millimetres.
  4. Note the tooth shape.Rounded and trapezoid-shaped teeth can share a pitch but won't fit the same pulleys. A side-on photo helps.
Pitch centre to centre
Pitch is measured from the centre of one tooth to the centre of the next.

Get an accurate pitch: measure across ten teeth and divide by ten, as 5mm and 5.08mm pitch belts look almost identical. Pitch multiplied by the number of teeth gives the length.

Common timing belt pitches
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

Roller chain

  1. Measure the pitch.Measure from the centre of one pin to the centre of the next. For accuracy, measure across ten pitches and divide by ten.
  2. Measure the roller diameter.This tells British Standard and ANSI chain apart where the pitch is the same.
  3. Count the strands.Simplex chain has one row of rollers, duplex two and triplex three.
  4. Count the pitches for length.Count the number of pitches, or measure the length and tell us the size of chain.
Pitch pin centre to pin centre
Pitch is the distance between the centres of two neighbouring pins.
Common roller chain sizes
Pitch British Standard Roller diameter ANSI Roller diameter
3/8" (9.525mm) 06B 6.35mm 35 5.08mm (bush, no roller)
1/2" (12.7mm) 08B 8.51mm 40 7.92mm
5/8" (15.875mm) 10B 10.16mm 50 10.16mm
3/4" (19.05mm) 12B 12.07mm 60 11.91mm
1" (25.4mm) 16B 15.88mm 80 15.88mm

British Standard or ANSI? They can share a pitch but aren't interchangeable. On 1/2" pitch chain, the most common mix-up, an 08B roller is 8.51mm and an ANSI 40 roller is 7.92mm. Where roller sizes are close, send us a photo and we'll confirm.

Send us your measurements

Email your measurements with a photo of the part, or give us a call. We'll work out what fits.

Opening hours Monday to Friday, 9am to 5pm