How To Measure Replacement Conveyor Rollers

Common Abbreviations

Our Terminology	Competitor Equivalant	Refers To
A	-	Axle Diameter, the diameter of the axle or size of the hex
BB / IF	BF, EL	Distance between inner walls of side frame.
EXTN	-	Extension of axle, how far the axle protrudes from the bearing
OA	OAL, AGL, AL	Over Axle, total length of axle
OB	OBL , OBP, OAC	Over bearing, length of roller including bearing bosses
RL	-	Roller length, the length of the roller without bearing bosses. Highly advise against using this
TD	-	Tube diameter, the diameter of the roller

Where to start?

Measure the frame if possible! Getting a measurement of the gap the rollers will be sitting in is extremely useful. By knowing this gap we know the limits of how long the roller can be and it makes it possible to work backwards to find other measurements you may be struggling to get.

Here are some quick examples of where BB/IF can help

Female threaded rollers – The axle length should equal the inside frame

Flatted rollers – the distance between flats should be equal to the inside frame

Spring loaded rollers – The over bearing would be a couple mm smaller than inside frame

Measuring the inside frame is also an easier measurement to get if you can get access to the track the roller will be going in as there is no awkward guessing of how far bearings boss protrude from the end of the roller.

Avoid Roller Length measurements if possible. While it may be tempting as it is an easy measurement to get by dropping a tape measure on the roller, this measurement is the leading cause of rollers being the wrong size when you’re unsure of measurements.

The rollers length doesn’t include bearing bosses and as the length of these bosses varies between manufacturers this can cause rollers be sized wrongly. The most common problems with giving roller lengths are as follows

It is assumed the measurement given is the over bearing, as such the roller will be undersized by anywhere from 5-10mm
The roller quoted has different length bearing protrusions so while you may be expecting a 3mm extension they could be 5mm meaning the roller is now 4mm over size and potentially locking up on the frame.

Even throughout our ranges we have rollers that have 2.5mm, 5mm and even rollers with no bearing protrusions so unless communicated clearly this can be a stumbling block.

Measuring Roller Diameter

Ideally you want a digital calliper to measure the roller diameter if possible as this will give you the most accurate reading however if you only have a tape measure it is still doable. If you are using a tape measure it is worth knowing some common sizes of tubes as it is unusual to have a roller not made from one of these. Below are some common examples off tube sizes

20, 30, 35, 40, 50, 50.8, 57, 60, 63, 70, 76, 80, 89, 102, 108, 127

If you are measuring your roller with a tape measure and you are seeing 64mm for example in all likelihood this would be 63mm or measuring 90mm it is likely 89mm. Knowing these common sizes is handy to track down a replacement roller.

Crowned or Parallel

If you have a roller which is used for tensioning or under belt use there is a chance that the roller is crowned to provide improved belt tracking. The first indicator that there may be a crown is if there are machining marks down the length of the roller. A easy check to see if a roller is crowned is to put it on a flat surface and press down on one end of the roller, if it rollers slightly (as crowns are only usually 1mm or less) it is possible that the roller is crowned.

To verify the roller is crowned put a digital calliper as close to the end of the roller as possible and take the measurement, then measure as close to the centre as possible and take this measurement. Finally measure as close to the end the other side. The measurements for either end should be the same and the centre slightly larger.

Usually, but not always, there is a parallel section in the centre of the roller with a taper either side down to the roller end. Put your calliper on the parallel section as slowly start to move to the end, when the reading starts to drop mark the roller and measure from the end to this mark to get the crown length, usually this is ~1/3 of the roller length.

Rubber covered or sleeved roller?

If you have a roller that is rubber covered or sleeved, the most important measurement is the diameter over the covering. Once we have this we can guess at a tube size that would but covered up to this diameter. So unless the covering is very thick the finish diameter will be fine, however please mention it is rubber covered/sleeved when getting a quote.

Diameters worth double checking

50 vs 50.8 (2”) – While only a small difference buying the incorrect roller could mean the roller is undersized and potentially not taking any load passed over it or oversized causing a small bump in the track. While workable it is always best to double check.

60 vs 63 – Two common sizes which at a glance can look similar but as with the above buying the incorrect one could mean the roller sits too high or too low and as the difference is 1.5mm it can be enough to cause issues.

Measuring Axle Size

Measuring the axle diameter is straight forward, just drop a tape/calliper on to the axle and take the reading. If the axle is a hex axle then make sure you measure flat to flat and not point to point.

Imperial vs metric axles

At AED rollers we don’t offer imperial axles as they do not suit our bearings with the exception of 5/8” (15.875mm) which we list as 16mm. All other sizes are standard metric sizes.

Stainless vs Mild Steel

When measuring a metal roller it can be obvious whether the roller is mild still / BZP / stainless steel however you should always check to be sure. To check place a magnet on the tube and then the axle, if the magnet sticks the you are working with mild steel, if it doesn’t then it is stainless.

When working with a plastic roller you should check to see if the axle is stainless too as some application require stainless and other mild steel. We offer both so make sure you check!

Measuring Over Axle

The over axle measurement is the length of the entire axle, sometimes this can be tricky to get as the axle is within the roller you cant lay a tape measure directly on the axle. Ideally if possible lay the roller on a table and place a flat heavy object up against the axle both ends and measure the distance between these.

Alternatively if you are certain of the OB measurements you can measure the extensions either side and add these together to get the OA

If all else fails you can try measuring by eye however depending on the type of axle this can be risky.

Low Risk – Spring loaded/Captive/Loose/Male Thread – as all these pass through the frame a couple of mm difference wont cause issues

Medium Risk – Cross drilled – depending on how close the hole sits against the frame, if tight to frame this is risky, if there is some play then measuring by eye should be ok.

High Risk – Flatted/Slotted/Female thread – As all of these sit against the frame measuring the OA wrong can result in rollers not fitting, if possible measure the gap the rollers will sit in to double check.

Measuring Over Bearing

The over bearing measurement is the total length of the roller without the axle. This means at any bearing bosses and protrusions must be taken into account. This measurement is vital as it ensures that the rollers will fit your existing frame without rubbing or too much play.

Ideally as mentioned before getting the distance between the frames is ideal as that provides a hard upper limit. If you don’t have access to the frame try and place the roller on top of two flat objects pressed up against the bearing boss then measure the distance between.

Alternatively if you are positive about the over axle measurement you can taken is and subtract the extensions either side to get the over bearing.

If you are measuring by eye it is safer to go 1 or 2mm shorter if unsure as this will guarantee fit the frame.

Measuring Types of Axle

Turn Down Male Thread

Spring Loaded AX1

If you’ve measured the over axle you are done. However make note on whether it is spring loaded one way or both ways

Flatted AX2

For flatted axles we need two measurements this is the across flat (AF) and the flat length (LG).

To measure the across flats place a calliper over the flats (so the jaws sit on both flats) this is your AF measurement

The flat length is measured by measuring the distance from the end of the axle to when the flat finishes. This is your LG measurement

If you have access to the frame you can double check if you wish, the across flats should be the same size / slighter smaller than the slot on the frame and the distance between the frame should be the same as OA – (FL*2).

D-Flatted AX3

Similar to flatted we need an across D-flat measurement (DF) and the flat length (LG).

To measure the across D-flat place one jaw of the calliper against the flat and the other jaw should sit on the diameter of the axle. This is you DF measurement

The flat length is measured by measuring the distance from the end of the axle to where the flat finishes. This is your LG measurement.

Slotted AX4

Very similar to the flatted axles, sometimes called closed flats we again need an across flats (AF) and flat length(LG), but also the distance of the inset of the slot (L).

To measure the across flats place a calliper over the flats (so the jaws sit on both flats) this is your AF measurement

To measure the flat length measure the width of the slot. Do not measure from the end of the axle only the gap which the slot creates.

Finally the get the inset distance measure from the end of the axle to the start of the slot, this is your L measurement.

Male Thread AX5

For a male threaded axle we need the size of the thread (M) and the length of the thread(LG).

Drop your callipers over the thread to get the size, if you are working in an environment where imperial measurements are still used double check if the thread size is imperial or metric. Once you have this you have your M measurement

Next to get the thread length simply measure how far the thread goes from the end of the axle, this is your LG measurement

As standard we supply male threaded axles loose (not fixed in placed) if it is fixed please let us know

Turn Down Male Thread AX6

For a turned down male threaded axle we need the same as above size of the thread (M) and the length of the thread(LG) with an added measurement of the turn down length (L).

Next to get the thread length simply measure how far the thread goes from the end of the axle, this is your LG measurement

Finally we need to get the length of the turn down, to measure this get the length from the end of the axle to where the turn down stops, this will be your L measurement

Turned Down AX7

The measurements needed for a turned down axle are the turn down diameter (D) and the length of the turn down (L)

To get the D measurements place a calliper over the turned down diameter to get your D measurement.

Next measure the length from the end of the axle to where the turn down ends, this is the length of your turn down and your L measurement

Female Thread AX8

When measuring female threaded axle we need the size of the thread (M) and the depth (LG)(optional).

The get the thread size either measure the bolt that fits in the axle or try a known bolt size to get your M measurement. If you don’t have the bolt but have a calliper putting the reverse jaws to get an inside measurement of the thread can be used to get your M measurement

PLEASE NOTE: If measuring the inside diameter using a calliper that the measurement will always be the drill size not the tap size. So for example a measurement of 8.5mm on a vernier is an M10 bolt. Double check this to make sure you don’t get an undersize thread.

To get an LG measure the depth of the thread, however if this isn’t possible we would D&T to a standard size, M8=20 deep M10=24 deep etc.

Loose Axle AX9

Good news, if you have the over axle length you don’t need to do anything else except tell us the axle is loose.

A loose axle means that the axle can completely slide out of the roller. If this isn't correct look at captive or spring loaded

Cross Drilled AX10

The measurements needed for a cross drilled axle are the diameter of the hole (D) and the inset of the hole (LC)

To get the D measurement you need to measure the diameter of the hole, as these holes are usually quite small getting a calliper in can be tricky but as these holes usually take R-Clips a measurement close enough should do.

To get the LC measurement we need the distance from the end of the axle to the CENTRE of the hole.

Captive AX11 & AX12

If you already have the over axle there is no more measuring you need to do, however please advise if you can see a circlip (AX11) or not (AX12 internal notch).