Rachel Drehmann model is a modified Houser San Francisco cup with an 18 bore...

Model/Description:

SCRDu: Rachel Drehmann cup underpart, threaded top, American shank.

SCRDu-EU: Rachel Drehmann cup underpart, threaded top, European shank.

SCRD-17.75mm: Rachel Drehmann rim.

Rim Options: Compatible with any 3/4 x 36 Giardinelli style screw rim having a junction diameter of .655-.660 inches. - See more at: http://www.siegfriedscall.com/collections/mouthpieces/products/san-francisco-french-horn-cup#sthash.9ZMMKFui.dpuf

The Shank is standard American taper or Morse 0... European is also in stock.

Cup Threading: Giardinelli 3/4 x 36 threads are standard.
Rim Options: Compatible with any 3/4 x 36 Giardinelli style screw rim having a junction diameter of .655-.660 inches.