Yamaha TRB 1005 Truss rod adjustment

I have search through old post and I couldn't find what I was looking for, so I will ask. I have owned my TRB 1005 for 4 years and I never had to adjust the trust rod always had great low action even through string changes. I was playing it today after I took it out of it's case and I noticed that I had to press the stings a lot harder than I normally do. To make a long story short it has a slight bow and I would like to know if anyone know the correct size allen tool use in this bass thanks for any help.

 

Thanks for the replies I do have sets of SAE and metric tools I just do not like putting improper sized tools on the TRUSS rod if I can avoid it, plus I am not able to get any tools I have into the cavity cleanly because of the space is tight against the body. I do know the proper spelling for truss, just look at my heading. Granted I made an error later in the text later, yes even an English teacher can make a mistake.