This adapter is made to easily allow installation of a oil pressure sensor that is 1/8" NPT, commonly used with Mychron oil pressure sensor. The metric threads for the block are M16X1.50 Sold individually
 
You DO NOT need to purchase the brass washer, when you take the plug out of the motor it will be on that plug. Purchasing the washer is an option if you would like to have a spare or replace with a new one.