The Damond Motorsports Turbo Oil Restrictor Bolt, reduces the oil feed to the factory K04 turbo, to help in preventing the common Mazdaspeed "smokey-turbo." Using proven and tested hole diamaters, the Damond Motorsports bolt allows proper oil feed to the factory K04 turbo, without over-oiling the turbo, and prevents oil seeping past the turbo seals into the exhaust. In addition 2 new OEM spec copper crush washers are included. This is a great, low-cost component, if you're looking to add a catless or more free flowing exhaust that would potentially result in more exhaust smoke.