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How to Measure a Rubber Belt
How are your belts measured?
The numerical portion of belt part numbers represent the total circumference (as if the the belt was cut and laid out flat on a ruler, without being stretched beyond its relaxed length.)
If your belt is broken at one spot, it is very easy to measure - just lay it alongside a ruler and measure its length. Deduct 5%-10% to compensate for stretching of the old belt.
If the belt is complete, you measure the length of the complete belt along a ruler and then double that measurement (deduct 5%-10% to compensate for stretching). See below: |
Specific Instructions for Complete Belts (not broken):
#1 - Get a ruler, 2 pens, and the old belt.
#2 - Pull belt just snug and measure length (don't stretch!)
 Now, double the length that you just measured! This is very, very important! 
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(If you haven't read the above step about multiplying the length you measured by 2, now would be a good time!)
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Belt above would have an approx 9" inside circumference (4.5" x 2).
Now, deduct 5% to 10% for stretching:
If you assume 5% stretching 9.0 - 0.45 ~ 8.6" IC
If you assume 10% stretching 9.0 - 0.90 = 8.1" IC
Choose a replacement belt between 8.0 and 8.7 inches
#3 - Measure belt thickness in inches.
Above belt is a little over 1/16" thick or around .075"
More on determining the thickness of square belts:
Our SBX series of belts (.090") are just a bit thicker than a U.S. Half Dollar (.085")
Our SBL series of belts (.075"-.079") are the thickness of a U.S. Nickel (.077")
Our SBM series of belts (.065") are the thickness of a U.S. Quarter (.066")
Our SBS series of belts (.046") are just a bit thinner than the thickness of a U.S. Dime (.051")
Our SBO series of belts (.039") are just a bit thicker than the thickness of a credit card (.033") So, above belt would be about .075" thick, and between 8.0 and 8.7 inches. If your exact size isn't in our database, pick a belt which is reasonably close. From our database, you'll see that we have a three belts which could work for our example above:
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Part
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I.C.
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Thickness
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Price ea
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SBL8.2
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8.2
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.075-.079
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$1.10
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SBL8.5
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8.5
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.075-.079
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$1.10
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SBL8.7
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8.7
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.075-.079
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$1.10
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Calculator for your use in determining belt size:
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