# of Set Screw holes: Describes the number of set screw holes on a drive pulley. Set screws are used to hold a pulley in place on a shaft, but they are not necessary if the operation includes a keyway.
Back Side Offset: The width from the center of the pulley to the backside edge of the hub or bore adapter.
Belts that fit: These are belts that fit into the groove of the v-groove idler or drive pulley. A belt is considered to fit into a pulley if both the following are true:
· The narrowest part of the belt does not touch the bottom of the V-groove.
· At least 3/4 of the belt fits inside the groove of the pulley. A slight overhang is acceptable.
IMPORTANT: A pulley can work with your belt but still not be appropriate for your system. For more information, check out our blog post, The Best Pulley for your V-Belt or contact us for assistance.
Finish: The finishing material used to prevent rusting in steel or cast iron products. Zinc Plating and powder coat provide the best rust prevention.
Frontside Offset: The width from the center of the product to the front edge of the hub, bearing, or bore adapter.
Groove Angle: The angle of the v-groove. This is largely governed by the diameter of the pulley, but can affect how deep in the groove your belt will ride.
Inside Diameter: The distance across the center hole, or bore, of the product. This dimension should match the diameter of your shaft or bolt.
Keyway: The width of the key used to anchor the pulley to a shaft. A negative keyway means this has an integral keyway, so no separate key will be needed to anchor the pulley.
Most shafts have the following standard keyway sizes:
| Shaft Size/ Inside Diameter | Standard Keyway Size |
| 1/2” (0.50) | 1/8” (0.125) |
| 5/8” (0.625) | 3/16” (0.187) |
| 3/4” (0.75) |
| 7/8” (0.875) |
| 1” | ¼” (0.25) |
| 1-1/8” |
Material: Describes what the product is made from. Plastic, aluminum, and diecast are softer, lighter, and do not rust. Steel and cast iron are meant for heavy-duty applications, but can rust in certain circumstances.
Material Thickness: Refers to the thickness of steel products only. This helps determine the overall sturdiness of the part. For Idler Pulleys, material thickness greater than 0.07” is considered Heavy Duty. For Drive Pulleys, thickness of 0.14” or greater is Heavy Duty.
Outside Diameter: The distance across the circle of the product, from outside edge to outside edge.
Overpin Diameter: An engineering dimension used to represent belt effective diameter. Cylinders or "pins" are placed at the top and bottom of the pulley's v-groove, the measurement is taken from the top of the upper pin to the bottom of the lower pin.
Pin Diameter: Diameter of the cylinder used to determine the belt with the best fit in v-belt drive and idler pulleys. Other belts may work with the pulley, but the fit into the v-groove will be different. The below chart shows the pin that corresponds to various belt sizes.
| Pin Diameter | Belt Type |
| 0.3750 | 3L |
| 0.4375 | 4L/A |
| 0.500 | 4L/A or 5L/B |
| 0.5625 | 5L/B |
| 0.7810 | C |
Stickout: The distance from the edge of the pulley’s flange to the edge of the bore adapter or hub. This is easiest to measure if the pulley is placed hub down on a flat surface. The stickout will be the space between the surface and the outside edge of the pulley. A negative stickout means that the pulley will lie flat on a surface with no gap.
Throughbore: Length of the bore, from one edge to the other. The Frontside Offset and Backside offset together equal the length of the throughbore.
Width: The distance from side to side of the pulley, across the area where the belt rides
For information on how to best measure your pulley, see our How to Measure Your Pulley page or contact us at [email protected] or 1-800-776-9315.
