LDV4 = inner diameter + .637" or 16.18mm
The LDV Model has a bit more room in the walls of the cup than the LD model has. The shorteness of the overall length with the #27 bore (.144 or 3.65mm) combined with a large back bore make this model the most free-blowing lead piece available. If you have been accustomed to playing on mouthpieces that have larger bore sizes, the LD models can offer the same open blow you've come to feel comfortable with and rely on. This set-up is easily the equivalent of a 25 bore with a Symphonic back bore, but with the extra boost for the range and shift in the timbre that a shallow cup can provide and that is required for lead playing or piccolo work.