Glossary of Friction Belt Drive Terms (Excerpt from JIS B 1860:2018)
2026/05/07
[Scope
] This standard specifies the terminology and definitions related to seamless V-belts, V-ribbed belts, V-pulley, and V-ribbed pulleys commonly used for power transmission. *This technical
document does not include any figures. Figures and the full text are available on the "Japan Industrial Standards Committee" website.
Table of Contents
A) V-belt
| Terminology | Definition | Corresponding English (for reference) |
|---|---|---|
| V-belt | A belt with a symmetrical trapezoidal cross-section composed of straight surfaces. The intersection where the bottom, side, and top surfaces meet may be formed with chamfers or rounded edges. | V-belt |
| Hexagonal belt | A belt with a hexagonal cross-section formed by connecting two isosceles trapezoids at their bases. | Hexagonal belt |
| Connected V-belt | A belt consisting of two or more V-belts arranged at equal intervals according to specified dimensions, with their upper ends joined by a connecting fabric. | joined V-belt |
| Pitch line | A reference line in the circumferential direction of a belt that maintains the same length even when the belt is bent. | pitch line |
| pitch plane | A surface composed of all pitch lines. | pitch zone |
| pitch width | The width of the belt at a given position on the pitch surface. The width remains unchanged even when the belt is bent in the direction of rotation. | pitch width |
| Top width | The wider dimension of the trapezoidal cross-section. | top width |
| Height | The height of the trapezoidal outline of the cross-section. | height |
| Relative height | A dimensionless characteristic calculated as the ratio of height to pitch width. [Note ] The four types of relative heights for V-belts are approximately as follows: Narrow V-belt: 0.9 ; Standard V-belt: 0. 7; Semi-thin V-belt: 0.5 ; Thin V-belt: 0.3 | relative height |
B) V-belt pulley
| Terminology | Definition | Corresponding English (for reference) |
|---|---|---|
| V-pulley | A pulley with one or more symmetrical V-shaped grooves on its outer circumference. | V-grooved pulley |
| Pulley groove angle | The angle between the two sides of the groove cross-section. | angle of pulley groove |
| Pulley groove pitch | The width of the pulley groove, which is the same as the pitch width of the belt used. | pitch width of pulley groove |
| Pitch circle diameter | The diameter of the pulley at the pitch width of the pulley groove. | pitch diameter |
| Circumference of the pitch circle | The circumference of a circle with a diameter equal to the pitch diameter. | pitch circumference |
C) V-belt drive
| Terminology | Definition | Corresponding English (for reference) |
|---|---|---|
| V-belt drive | A transmission system consisting of two or more V-belts and one or more V-belt pulleys. The belt transmits power by contacting only the sides of the pulley grooves, rather than the bottom. | V-belt drive |
| Speed ratio | The ratio of the angular velocities of the pulleys, calculated from the ratio of their pitch circle diameters. Slip and belt deformation are not taken into account. | Speed ratio |
D) System based on datum width
| Terminology | Definition | Corresponding English (for reference) |
|---|---|---|
| Datum Width | A specified value for the groove width defined by the shape of a V-belt, with no tolerance. It is the standard width of the driving surface in the cross-section of a V-pulley’s V-shaped groove, and remains constant even if the groove angle of the pulley is changed. Generally, it corresponds to the pitch width of the V-belt. | datum width |
| Datum diameter | The diameter at the datum width on a V-belt pulley. | datum diameter |
| datum circumference | The circumference of a circle with the same diameter as the datum diameter. | datum circumference |
| DLD | The radial distance between the pitch circle diameter and the datum diameter. [Note ] DLD is used as a correction factor to calculate the speed ratio when a datum line is given. [Note] When the pitch surface of a V-belt and the datum width of the pulley are aligned, DLD is 0. | datum line differential |
| Datum length | The length obtained by adding twice the center-to-center distance between two pulleys of equal datum diameter, when the V-belt is mounted on them under constant tension, to the datum circumference of one pulley. This is typically used to indicate the belt length. | datum length |
E) System based on effective width
| Terminology | Definition | Corresponding English (for reference) |
|---|---|---|
| Effective Width | The groove width specified for each V-belt type; this is a fixed value with no tolerance. The maximum width of the groove on the straight section of the drive surface within the cross-section of a V-pulley’s V-shaped groove . Typically, this corresponds to the outermost part of the straight section of the groove. | effective width |
| Effective diameter | The diameter of the pulley at the effective width of the groove. | effective diameter |
| effective circumference | The circumference of a circle with the same diameter as the effective diameter. | effective circumference |
| ELD | The radial distance between the pitch circle diameter and the effective diameter. [Note ] ELD is used as a correction factor to calculate the gear ratio when the effective diameter is given. | effective line differential |
| Effective belt length | The length obtained by adding twice the center-to-center distance between two pulleys with equal effective diameters, when a V-belt is mounted on them under constant tension, to the effective circumference of one pulley. This is typically used to indicate the belt length. | effective length |
F) V-ribbed belt
| Terminology | Definition | Corresponding English (for reference) |
|---|---|---|
| V-ribbed belt | A belt with ribs shaped similarly to the grooves of a pulley, designed to engage with pulleys having multiple grooves and transmit power through friction. | V-ribbed belt |
| Pitch line | A reference line in the circumferential direction of the belt that maintains the same length even when the belt is bent. | pitch line |
| Pitch plane | The surface formed by all pitch lines. | pitch zone |
| Effective belt length | The length obtained by adding twice the center-to-center distance between two pulleys ( when a V-ribbed belt is installed on them with equal tension) to the effective circumference of one pulley. This is typically used to indicate the belt length. | effective length |
| Free belt length | The belt length measured using 10% of the measurement force during effective belt length measurement. Applies only to elastic belts. | free length |
| Drive layout length | In a drive layout, the length of the belt connecting the effective diameters of the pulley and idler when their centers are in their reference positions. Applies only to elastic belts. | drive length |
| Elongation ratio | The value obtained by subtracting the belt free length from the drive layout length and dividing by the belt free length. Applies only to elastic belts . | elongation |
| Rib pitch | The distance between the centers of two adjacent ribs. | rib pitch |
| Standard belt width | The nominal dimension of the belt in the width direction. The value obtained by multiplying the rib pitch by the number of ribs. | nominal belt width |
| Variation in center-to-center distance | The difference between the maximum and minimum center distances when measured with a length measuring device under specified conditions. | centre distance variation |
| Elastic belt | A specialized V-ribbed belt designed to be stretched and installed in layouts with a fixed center distance. | elastic belt |
| Terminology | Definition | Corresponding English (for reference) |
|---|---|---|
| Effective width | The groove width specified for each type of V-belt; this is a fixed value with no tolerance. It refers to the maximum width of the groove on the straight section of the drive surface within the cross-section of the V-groove on a V-pulley. It is typically located at the outermost edge of the straight section of the groove. | effective width |
| Effective diameter | The diameter of the pulley at the effective width of the groove. | effective diameter |
| effective circumference | The circumference of a circle with the same diameter as the effective diameter. | effective circumference |
| ELD | The radial distance between the pitch circle diameter and the effective diameter. [Note ] ELD is used as a correction factor to calculate the gear ratio when the effective diameter is given. | effective line differential |
| Effective belt length | The length obtained by adding twice the center-to-center distance between two pulleys with equal effective diameters, when a V-belt is mounted on them under constant tension, to the effective circumference of one pulley. This is typically used to indicate the belt length. | effective length |
G) V-ribbed pulley
| Terminology | Definition | Corresponding English (for reference) |
|---|---|---|
| V-ribbed pulley | A pulley with multiple V-grooves spaced at equal intervals, all sharing the same pitch circle diameter. | V-ribbed pulley |
| Flat pulley | A cylindrical pulley used on the back or ribbed side of a belt. | Flat pulley |
| Pulley groove | Several V-shaped grooves formed on the outer circumference of the pulley where the belt ribs engage. | pulley groove |
| Groove pitch | The distance between the centers of two adjacent pulley grooves. | groove pitch |
| Radius of the pulley tip | The radius of the rounded portion at the crest formed between two adjacent grooves. | transitional radius |
| Radius of the rounded bottom of the pulley groove | The radius of the section at the bottom of the groove where it connects to the groove sidewall. | groove bottom radius |
| Pulley groove angle | The angle formed by the two sides of the groove cross-section. | angle of pulley groove |
| Pitch circle diameter | The diameter of the pulley at the belt pitch line when the belt is wrapped around the pulley. | pitch diameter |
| Circumference of the pitch circle | The circumference of the circle with a pitch diameter. | pitch circumference |
| Effective diameter | The diameter of the pulley at the top of the groove when the radius of the pulley's tip rounding is at the minimum tolerance. | effective diameter |
| Outer diameter | The diameter of the pulley at the top of the groove. | outer diameter |
| Effective circumference | The circumference of a circle with the same diameter as the effective diameter. | effective circumference |
| ELD | The radial distance between the pitch circle diameter and the effective diameter. [Note ] ELD is used as a correction factor to calculate the gear ratio when the effective diameter is given. | effective line differential |
H) V-ribbed belt drive
| Terminology | Definition | Corresponding English (for reference) |
|---|---|---|
| V-ribbed belt drive | A drive system consisting of a single V-ribbed belt and two or more pulleys, at least one of which is a V-ribbed pulley. The axes of all pulleys are perpendicular to the plane formed by a single pitch line. | V-ribbed belt drive |
| Speed ratio | The ratio of the angular velocities of the pulleys, calculated from the ratio of their pitch circle diameters, without taking into account slippage or belt deformation. | Speed ratio |
| Rated transmission capacity | The power that a single V-belt or V-ribbed belt can transmit for a given period when wrapped 180° around a specified pulley at a specified tension. | power rating |
I) Belt Tension
| Terminology | Definition | Corresponding English (for reference) |
|---|---|---|
| Belt Length Measurement Tension | The belt tension when the specified measuring force is applied during effective belt length measurement. | measuring tension |
| Steady-state tension | The belt tension after operation for a specified period under prescribed conditions. Limited to elastic belts. | stabilized tension |
| Maximum tension during installation | The maximum tension generated when installing the belt. Applies only to elastic belts. | installation tension |
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