Brawley 5 string truss rod adjustment tool

[Tabmo]

Hello. I bought a Brawley five string bass several years ago and never played. I decided to break it out today and discovered the truss rod needs to be adjusted. I did not get the truss rod adjustment tool with the bass and cannot seem to figure out what to use on it. Can anybody tell me what to use to do this with? Thanks in advance for your help.

 

[Dluxe]

It is either a 4 or 5 mm hex wrench. I can't remember which but it is metric for sure.