GR trumpet mouthpiece 66C used for brief trial period, in mint condition.

About the size of a Bach 3C.  Has the larger GR 3 backbore.  Medium large cup with 0.66 in (16.76mm) cup diameter.

Has a more open throat entrance and is more free blowing.  Suitable for strong player in orchestral setting.

The tone is richer and darker with great volume of sound.