Most customers use a ring with a 45-mm diameter. However, other diameters are available. The following is a 4-step procedure to help you determine the right diameter for you.

• Take a string some 30 cm (12 inches) long, and place it around you’re your scrotum and penis. Remember not to use elastic string, as this would skew the measurements.
• Make a double knot: the string should be tight enough to make it difficult for you to slip a finger under it, yet not so strong as to cut off the blood flow. Leave the string on for 5 minutes,
• to make sure it is the right diameter. Cut the string with a pair of scissors, taking care not to hurt yourself while doing so.
• Measure the length of the string, and consult the following table to learn which is the right diameter for you.

Alternatively, if you have worn a CB-2000, CB-3000, CB-6000, or Curve, and know your ring size, the following would be a rough equivalent chart

If you have worn a 1-1/2" ring, get the 40mm ring size
If you have worn a 1-5/8" ring, get the 40mm or 45mm ring size
If you have worn a 1-3/4" ring, get the 45mm ring size
If you have worn a 1-7/8" or larger ring, get the 50mm size