Metric Wrapped V-Belts allow more power per belt and therefore permit wedge belt drives. They are also matched, oil-heat resistant and static dissipating. As a general rule, the numbering system starts by SP letters, followed by the cross-section designations Z-A-B-C and numbers giving the pitch length. However, some belts will either identify the length by adding the following letters after the number, LA for outside circumference LI for inside circumference, or LW for pitch circumference.