Same width, different section
A and SPA are both about 13 mm across the top, but SPA is 10 mm high against 8 mm and is designated by the datum length. B and SPB, C and SPC pair the same way.
Reference tool — not inspection
Identify the belt before it goes in an RFQ.
Belt
A designation or a measured section.
A designation is read whole, with its length; for a measurement the top width and the height are enough. Put an offered replacement in the second field, and the reader checks the section, the bands or ribs and the length. The result updates as you type.
Examples:
Replacement check
On the designations alone: the maker’s catalogue and the pulley decide.
All 130 engineering tools
V-belts for compressors, fans, generators and pumps are ordered by section and length, and the same number in a designation means different things: an inside length on an A belt, a datum length on an SPA, an outside length in tenths of an inch on a 5V. Enter the print on the belt or a measured section, and the tool names the section and all three lengths.
The length in the designation is exact; the other two are converted with the makers’ offsets and marked as approximate, because makers’ conversions differ by a few millimetres. The print on the belt settles it.
Why belts get confused
Section, three lengths, two series.
Three lengths on one belt
Inside, datum and outside lengths differ by tens of millimetres: an A belt with a 1067 mm inside length has a datum length of about 1097 mm and an outside length of about 1117 mm.
Inch and metric names
A42 is a 42 in inside length, 5V1000 a 100 in outside length, SPA 1250 a 1250 mm datum length. The same number means different things in each series.
| Section | Width × height, mm | Number in the designation | Conversion, mm |
|---|---|---|---|
| Z (Z/10) | 10 × 6 | inside length Li | Ld = Li + 22, La = Li + 38 |
| A (A/13) | 13 × 8 | inside length Li | Ld = Li + 30, La = Li + 50 |
| B (B/17) | 17 × 11 | inside length Li | Ld = Li + 40, La = Li + 69 |
| C (C/22) | 22 × 14 | inside length Li | Ld = Li + 58, La = Li + 88 |
| D (D/32) | 32 × 20 | inside length Li | Ld = Li + 75, La = Li + 126 |
| SPZ | 9.7 × 8 | datum length Ld | Li = Ld - 38, La = Ld + 13 |
| SPA | 12.7 × 10 | datum length Ld | Li = Ld - 45, La = Ld + 18 |
| SPB | 16.3 × 13 | datum length Ld | Li = Ld - 60, La = Ld + 22 |
| SPC | 22 × 18 | datum length Ld | Li = Ld - 83, La = Ld + 30 |
| 3V | 9.5 × 7.9 | outside length, tenths of an inch | — |
| 5V | 15.9 × 13.5 | outside length, tenths of an inch | — |
| 8V | 25.4 × 22.2 | outside length, tenths of an inch | — |
Conversions are approximate, from Optibelt’s offsets (classical) and Ametric’s (narrow). V-ribbed belts: rib pitch PJ 2.34, PK 3.56, PL 4.70, PM 9.40 mm; the number in the designation is the effective length in mm.
Sources
Classical sections Z to D (ISO 4184 / DIN 2215): length offsets from Optibelt’s datasheet for each profile; Ametric’s table gives the same outside offsets. Narrow SPZ to SPC (ISO 4184 / DIN 7753) and cogged XPZ to XPC: offsets from Ametric’s table, with Rubena’s catalogue giving the same outside offsets for SPA, SPB and SPC. Section width and height: Ametric and Optibelt’s datasheets. Inch designations A to D and 3V, 5V, 8V: Texas Belting’s identification guide and McMaster-Carr. Rib pitch of V-ribbed belts: Gates Micro-V listings and Optibelt RB.
Before you send the belt
Questions about belts in an RFQ
What is the difference between Li, Ld and La?
Li is the inside length, Ld the datum length on the line of the tension cords, La the outside length. Classical belts (Z, A, B, C, D) are designated by Li, narrow belts (SPZ to SPC, XPZ to XPC) by Ld, and 3V, 5V and 8V by the outside length in tenths of an inch. An SPA belt is about 18 mm longer outside than its datum length; an A belt’s datum length is about 30 mm more than its inside length.
Is an SPA belt the same as an A belt?
No. Both are about 13 mm across the top, but SPA is 10 mm high against 8 mm, runs in its own pulley groove and is designated by the datum length, not the inside length. Measure the height or read the print on the belt.
What does XPB mean?
XPB is the cogged raw-edge version of SPB: the same designation by datum length and the same pulley grooves. AX, BX and CX are the cogged versions of the classical A, B and C.
How is 6PK1200 read?
Six ribs of the PK profile, 3.56 mm rib pitch, on an effective length of 1200 mm. An inch code such as 453J6 is 45.3 in, PJ profile, six ribs.
What if nothing matches?
A used belt wears narrow at the top. Measure the pulley groove, count the belts on the drive and send the print on the belt with a photograph. Light-duty 3L to 5L belts, variable-speed belts and toothed timing belts are outside this tool.
Belt identified?
Send the designation with the photograph.
An identified section is a cross-check on the print or the measurement, not proof. Give the print on the belt, the number of belts on the drive and the machine, and Vessel Core checks them against each other before an offer goes back.
Buyer tools
