The "gray" rubber cap which covers and protects the read switch (used on models- 301, 361T, 369 and 310T.
Read switch cap replacement kits are available through the web store www.xrite.com or by calling 888-826-3044
If you have the 369, 361T or 310T use part number 361-100-KIT
If you have a 301 which use Part number 301-100-KIT.
Installation instructions are included with the kit.