Firstly, look for identifying numbers and letters marked on the belt. These numbers indicate a standard trade size and will help in indentifying the specifics of the belt.
Secondly, if there is no trade size indicated on the belt do the following:
Measure the width of the belt
Note the construction of the belt. Rubber construction is extremely flexible while a polyurethane construction is plastic like and has little flexibility
Measure the pitch (see diagram). This is the distance in millimeters (mm) between the center of the crown of one tooth and the center of the crown of the tooth next to it.
Pitch
Timing Belt Tooth Profile / Pitch
Inches
Metric
CTD
C8M / CTD
8mm
0.315"
8mm
C14M / CTD
14mm
0.551"
14mm
HTD
3M / HTD
3mm
0.118"
3mm
5M / HTD
5mm
0.197"
5mm
8M / HTD
8mm
0.315"
8mm
14M / HTD
14mm
0.551"
14mm
20M / HTD
20mm
0.787"
20mm
PolyChain GT
5M / PCGT
5mm
0.197"
5mm
8M / PCGT
8mm
0.315"
8mm
14M / PCGT
14mm
0.551"
14mm
PolyChain GT HTD
14M / PCGT HTD
14mm
0.551"
14mm
PolyChain GT2
8M / PCGT2
8mm
0.315"
8mm
14M / PCGT2
14mm
0.551"
14mm
PowerGrip GT2
2MR / PGGT2
2mm
0.079"
2mm
3MR / PGGT2
3mm
0.118"
3mm
5MR / PGGT2
5mm
0.197"
5mm
8M / PGGT2
8mm
0.315"
8mm
14M / PGGT2
14mm
0.551"
14mm
20M / PGGT2
14mm
0.787"
20mm
RPP
5M / RPP
5mm
0.197"
5mm
8M / RPP
8mm
0.315"
8mm
14M / RPP
14mm
0.551"
14mm
20M / RPP
20mm
0.787"
20mm
STD
S8M / STD
8mm
0.315"
8mm
Trapezoidal (Inch Pitch)
2/25" MXL
0.080"
0.080"
2.032mm
40 D.P.
0.0816"
0.0816"
2.07mm
1/5" XL
0.200"
0.200"
5.08mm
3/8" L
0.375"
0.375"
9.525mm
1/2" H
0.500"
0.500"
12.7mm
7/8" XH
0.875"
0.875"
22.23mm
1-1/4" XXH
1.250"
1.250"
31.75mm
Trapezoidal (Metric Pitch)
T2.5
2.5mm
0.098"
2.5mm
T5
5mm
0.197"
5mm
T10
10mm
0.394"
10mm
T20
20mm
0.787"
20mm
Trapezoidal (Metric Pitch)
AT5
5mm
0.197"
5mm
AT10
10mm
0.394"
10mm
AT20
20mm
0.787"
20mm
Note: Belt Tooth Profile Abbreviations
CTD
ContiTech - Conti Torque Drive
HTD
High Torque Drive
PGGT
Gates - PowerGrip GT
PGGT2
Gates - PowerGrip GT2
PCGT
Gates - PolyChain GT
PCGT HTD
Gates - PolyChain GT HTD
PCGT2
Gates - PolyChain GT2
RPP
Carlisle - Reinforced Parabolic Profile
STD
Super Torque Drive
Note the shape of the pulley teeth (tooth profile); if the valley between the teeth is curved than it is an HTD style belt. If the valley between the teeth is flat than it is and PolyChain GT style belt. You should also look for identifying numbers and/or letters on the pulleys themselves to help in the belt tooth profile identification.
Count the number of teeth on the belt. I suggest marking one tooth on the belt with some sort of identification so that you have a starting point for the tooth count. You can also measure the length of the belt from end to end if the belt is broken. If the belt is in place measure the circumference of the belt (distance around the outside edge of the belt)
From these pieces of information a replacement belt can be identified.
Lastly, if you are changing any of the pulleys in the power transmission drive than the belt length is more than likely to change also. The following information will be needed to determine the correct belt length
Center to center distance between the shaft the driver pulley is fixed to and the shaft the driven pulley is fixed to. This measurement is taken from the center of the shafts. There should be two (2) measurements for this since the majority of timing belt drives has a means in place for tensioning the belts. The two distances required will have one of the shafts in the all the way forward position and the other in the all the way backward position.
Center to center distance all the way FORWARD
Center to center distance all the way BACKWARD
Count the number of teeth on both pulleys. I suggest marking one tooth on the pulleys with some sort of identification so that you have a starting point for the tooth count
From these pieces of information a replacement belt can be identified.
