The Cup Spacer raises the floor of the lower boom mount to allow for clearance of a boom pole with a side exit XLR cable. 
 
It's easily removable with a flat tip screwdriver in the visible slot provided. 
 
This is free upon request with any future or past order. Please message me if you've had a past order and would like one. There are two cup depths so just let me know which cart you purchased the mount for. 
 
Thanks!