FHP V-Belt Sizes: 2L, 3L, 4L and 5L

FHP stands for fractional horsepower. The 2L, 3L, 4L and 5L belts are the light duty V-belt sections, published for light duty drives using a single belt and ideal for fan applications. A belt number states two things and nothing else: the section, which fixes the cross-section of the belt and the groove it seats in, and the outside length. This guide gives the width and depth of each section, shows how the number is read, sets out where a 4L or 5L belt may be replaced by an industrial section, and lists the sheave grooves each section runs in. The belts themselves are in the belts category and the sheaves cut for them in FHP sheaves.

What do 2L, 3L, 4L and 5L mean on a V-belt?

They are the four fractional horsepower belt sections, and the section fixes the cross-section of the belt. A 2L belt is 9/32 inch across the top, a 3L is 3/8 inch, a 4L is 1/2 inch and a 5L is 21/32 inch, and each section has its own depth as well. The letter and digit are not a size in themselves: they are the section name, and the table below is what each one measures.

The top width is what identifies a belt whose markings have worn off. Measure across the top with calipers, well clear of a cracked or glazed stretch, and read the section from the table. Two of the four widths are shared with an industrial section: a 4L and an A belt both measure 1/2 inch, and a 5L and a B belt both measure 21/32 inch. Depth separates the second pair, a 5L at 0.375 inch against a B at 7/16 inch, but not the first, where a 4L at 0.312 inch and an A at 5/16 inch come to the same figure. On an unmarked 1/2 inch belt it is the substitution rule below, not a measurement, that decides which one is safe to fit.

How do you read an FHP belt number like 4L300?

The first two characters are the section and the remaining digits are the outside length in tenths of an inch. A 4L300 is a 4L section belt with a 30.0 inch outside length, and a 5L500 is a 5L section belt 50.0 inches around the outside. Outside length is the figure a tape run around the outside of the belt gives.

Pitch length, the length along the cord line that a drive calculation uses, is shorter than the outside length and is published against every stock size. It runs 0.4 inch inside the outside length on a 2L, 0.7 inch on a 3L, 1.0 inch on a 4L and 1.2 inches on a 5L.

Stock sizes step by one inch of outside length over most of the range, which is why the last digit is normally a zero. A few half-inch sizes exist, and they are written the same way: a 2L325 is 32 1/2 inches outside, and a 4L225 is 22 1/2 inches. The stock sizes run from 2L150 to 5L1000.

What is the difference between a 3L and a 4L belt?

A 3L belt is 3/8 inch wide and 0.219 inch deep; a 4L belt is 1/2 inch wide and 0.312 inch deep. The 4L is the larger cross-section of the two and the one that shares a groove with the A section, so it carries the heavier drive. They are not substitutes for one another on a drive, though many single groove sheaves cut for a 4L or A belt may also be used with a 3L.

The sheave already on the machine decides which you need. A sheave cut for a 4L or A belt that may also be used with a 3L publishes a datum diameter for the A belt and a pitch diameter for the 3L, because the smaller belt sits lower in the one groove. The AK64X1 is a 6.25 inch outside diameter cast iron sheave of that kind: its groove is listed for a 4L or A belt and for a 3L, with a 6.00 inch datum diameter on the A belt and a 5.66 inch pitch diameter on the 3L. A 3L190 on that sheave and a 4L belt on that sheave run at two different effective diameters, so the driven speed changes with the belt you fit.

Can a 4L belt be replaced with an A or AX belt?

Yes, in that direction only. A 4L or 5L belt may be substituted with the matching A or B wrapped belt or the matching AX or BX notched belt, but an A, B, AX or BX belt may not be substituted with a 4L or 5L. A 4L300 can be replaced by an A28 or an AX28, and a 5L500 by a B47 or a BX47; going the other way puts a light duty belt on a drive specified for an industrial one.

The equivalent is not the same length. The 4L number states an outside length in tenths of an inch while the A and AX numbers carry their own length, so a 4L300 at 30.0 inches outside cross references to an A28 at 30.2 inches. Check the length column rather than converting the number yourself.

The 2L and 3L sections have no such equivalent. No cross reference is published from either of them to an industrial section, so a worn 2L or 3L is replaced with the same section. If the belt on the machine is unmarked and its width falls between two sections, send the width, depth and outside length through the cross reference form and we will confirm the section before you order.

Which FHP and classical belt sizes do we stock?

We stock 517 sizes across the 8 sections below, and every one of them is a link to that belt's own product page. The fractional horsepower sections come first, then the wrapped A and B sections and the notched AX and BX sections a 4L or 5L cross references to. Find the row for your section and read along it to the length you need: the numbers climb by length, so the shortest belt in a section is first and the longest last.

The rows state what we hold now, not every size a section publishes, and a section we hold one size in is one belt rather than a range. The narrow 3VX, 5V, 5VX, 8V and 8VX sections, the double-V AA and BB sections and the synchronous belts are not in this table; they sit alongside these in the belts category with the rest of the range.

How do FHP belts compare with A, B, 3V, 5V and 8V sections?

The classical sections A, B, C and D and the narrow sections 3V, 5V and 8V are the industrial belts, built for single and multiple belt drives well above the fractional horsepower range. The FHP sections are published for light duty single belt drives; the classical A, B and D sections cover 1 to 500 horsepower and the narrow 3V, 5V and 8V sections 1 to 1000. The narrow sections are deeper for their width, which is what lets a 3V belt at 3/8 inch wide carry far more than a 3L belt of the same width.

Numbering differs as well. A classical belt such as an A28 carries a belt reference number rather than a length in tenths, so its 30.2 inch outside length has to be read from the size tables. A narrow belt such as a 5VX1180 does state its outside length in tenths, 118.0 inches, after the section. The full range of industrial sections sits in the V-belt sheaves category alongside the sheaves cut for them.

What does the X in a belt part number mean?

An X in the part number marks a notched belt. AX, BX, CX, 3VX and 5VX are the notched Gripnotch profile; A, B, C, 3V and 5V without the X, and every FHP section, are wrapped. The two are different constructions rather than different sizes, so an AX28 and an A28 fit the same groove and the same length of drive.

A wrapped belt carries a fabric cover over the body, which is what gives it smooth, quiet running. A notched belt is precision molded with a raw edge and notches molded extra deep, so it bends more freely and delivers more horsepower in less space than a wrapped belt of the same section; it is also the belt to move to when a drive has insufficient arc of contact and the center distance cannot be increased. The materials differ too: the FHP belts are rubber and the classical Gripbelts neoprene, and a 3L190 is rated from -32 to +140 degrees Fahrenheit, while the notched belts are EPDM and are rated from -60 to +250.

Two limits are published on the sheaves rather than the belts. Cast iron sheaves cut for a 4L or A belt with a bore of 1 inch and under are not to be used at notched belt ratings, and the combination groove sheaves cut for 4L or A and 5L or B are not to be used at B section notched belt ratings.

Which sheave groove does an FHP belt run in?

Match the section to the groove listing printed on the sheave. The published groove listings are 3L, 4L or A, and 5L or B, and most stock sheaves are cut to take more than one section in a single groove. Sheaves in the FHP sheaves category state their groove listing as a specification, so the belt section can be checked before ordering.

The largest groups are the single groove sheaves listed for a 4L or A belt and a 3L, such as the AK64X1, and the combination groove sheaves listed for a 4L or A belt and a 5L or B. A third combination groove adds 5V to the same two. The single groove variable pitch sheaves are published for 3L, 4L, 5L, A, B and 5V belts in one adjustable groove, but the diameter range is published per sheave size rather than for the whole family, so check the section against the individual sheave before ordering one.

There is no 2L groove on any stock sheave, so a 2L belt runs on the sheave supplied with the equipment it came from. For the other three sections, confirm the groove listing on the sheave against the belt section, and remember that a sheave listed for two sections publishes a different diameter for each: fitting the other section changes the drive ratio as well as the fit.