These are traditional size Schilke mouthpieces that are specially made for tenor and bass trombones having a large Remington shank style receiver. Examples of these trombones include Elkhart, Indiana production of the Conn 8H, 88H, 60H 62H, 70H-73H and others. The new Generation II Conn 88H trombone with removable leadpipes includes one that is tapered to fit this style of mouthpiece, and is labeled "R" for Remington. Otherwise, these trombones are fairly rare, so this mouthpiece is for the aficionado who wants a properly fitting period style mouthpiece for his vintage trombone.
What's the Diff?
The common large shank trombone mouthpiece has a Morse taper shank, while these special Schilke mouthpieces are a slightly slower taper called Brown & Sharp, resulting in a longer shank.