This is a hard rubber example. According to Theo Wanne's website, "these hard rubber mouthpieces are among the best ever made"! There is an early and late version, this being the more desirable early version. It has very scooped inner side walls and a large round chamber.
The serial number 87858 is stamped on the side. It is also stamped S4, indicating a short facing curve and #4 tip opening. It appears however that it has been worked on at some point. The horizontal mill marking are visible all the way up the side rails until about half an inch before the tip, at which point it is smooth. This would indicate an alteration of the tip opening.
It also looks like the baffle was worked on just behind the tip. I have no idea who did the work, but it looks to have been skillfully done, however, you may wish to have it checked out by a trusted mouthpiece re-facer of your own choosing and adjusted if necessary. The tip opening currently measures. It is in very good condition with a perfectly smooth tip, table, and side rails.There are no cracks, and no tooth indentations. It is still black and shiny. The item "BRILHART PERSONALINE S4 ALTO SAXOPHONE MOUTHPIECE EARLY HARD RUBBER SERIAL #" is in sale since Friday, August 17, 2018. This item is in the category "Musical Instruments & Gear\Wind & Woodwind\Parts & Accessories\Mouthpieces". The seller is "greatlakeswinds" and is located in Milwaukee, Wisconsin. This item can be shipped worldwide.