
Fractional horsepower sheaves are the small end of the V-belt range, cut for the 3L, 4L and 5L light-duty sections and the A and B sections that share their grooves, in one and two grooves only. The naming is regular. An AK sheave is a cast iron single groove sheave for an A section belt with a finished bore; the same sheave as AKH is bored for an H Split Taper bushing. BK and BKH are the same pair in a combination groove that takes 4L or A and 5L or B belts. Variable pitch types in the same family have a movable flange, so the pitch diameter and with it the drive speed can be trimmed on site by opening the groove a measured number of turns.
Also known as: fractional horsepower sheaves, fhp pulleys, ak sheaves, bk sheaves
Series in this category
Related guides: FHP V-belt sizes, V-belt sheave sizes, Split taper bushing sizes, Cross-reference help
| Specification | What it means |
|---|---|
| Belt section | The sections the groove takes, listed as 3L, 4L or A, 5L or B, and as combinations such as 4L or A with 5L or B. |
| Product type | FHP finished bore, FHP bushed, or FHP variable pitch, which is how the sheave mounts and whether its groove is adjustable. |
| Bore and bore code | The finished bore size in inches and the internal bore code the listing carries for it, such as ARK or ARV. |
| Keyway size and set screw thread | The keyseat cut in a finished bore and the set screw that retains it, with a tightening torque given in inch-pounds. |
| Datum diameter and pitch diameter | The effective diameter for each section the sheave takes. Ratio and belt length calculations use these figures. |
| Turns open for minimum pitch diameter | On a variable pitch sheave, how far the movable flange opens to reach the smallest pitch diameter it will hold. |
It reads as a single groove cast iron sheave for an A section belt with a finished bore. The number that follows is a nominal diameter reference and any figure after an x is the bore, so AK64 x 1 is that sheave at the AK64 pitch diameter with a 1 inch bore. Adding an H, as in AK89H, changes the hub to take an H Split Taper bushing instead of a finished bore.
On many of them, and the listings mark which. The AK and BK families are grooved for 4L or A belts, and the tables state where a 3L belt may also be used in the same groove. Where the table does not mark it, the groove is too wide for a 3L belt to seat properly and the belt will ride low and slip.
Open the movable flange. Turning it out widens the groove, the belt rides deeper and the effective pitch diameter falls, which reduces the driven speed if the adjusted sheave is the driving one. The listings state the turns open that correspond to the minimum pitch diameter for each belt section, so the setting is made to a count of turns and can be repeated exactly.
When the drive needs more than a single light-duty belt or more than about three horsepower. Fractional sheaves are stocked in one and two grooves only and are cut for the light 3L, 4L and 5L sections, so a drive needing three or more belts, or one of the narrow 3V, 5V or 8V sections, moves into the V-belt sheave range instead.