Here is an original condition, Selmer "Soloist" C*. This piece measures .063" on my gauge.
The short shank soloist model alto pieces were offered by Selmer in mid 50's for sale on their own and also as the mouthpiece designed for and included with the vaunted Mark VI saxophones.
These are special pieces as their unique geometry performs well in many styles of music, unlike the current generation of C* pieces. The straight side walls, that open up in a complex shape to a sort of 'cathedral' or horseshoe shape allows for brilliance but also warmth. This piece would be an ideal candidate to open to a more contemporary size for a jazz or commercial player.