That’s a 3/4 open spacer , I found running this that the idle smoothed out a bit but did shift the rpm up a little aswell. Reason for running the wood spacer is to eliminate as much heat away from the sniper due to the ecu being mounted at the front and there has been cases where the heat has caused malfunction in these units. Just ticking boxes to eliminate any issues. In all honesty I have been using this unit for 15 months now and it’s been faultless , instant throttle response and drivability has been great. People are using the spacer to eliminate the whistle sound they sometimes produce. You just need to adjust the iac properly.