CM246
The XUI1620L is the diamond-bolt-pattern master cylinder shared across the 996-generation Porsche 911 and Boxster as well as several B5-platform Audi/VW models, machined and polished to match the factory finish.
Detailing on this unit includes a polished cylinder body and a diamond 4-bolt mounting pattern, and is machined precisely to a 23.81mm bore, a Φ46/102/2-Φ21.8 mounting pattern, and M12 X 1.0, M12 X 1.0 port threads.
This part number is tied to 1999-2005 Porsche 911, 2003-2004 Porsche Boxster, 1997-2000 Porsche Boxster, 1996-1999 Audi A4, and 1996-1998 Audi A4 Quattro, plus 3 further listed applications. The relevant OE numbers are 8D0611021A, 8D0611021B, and 99635591000. It's also cross-listed under DORMAN part numbers for easier sourcing.