Can't Thread Fuji Cube Bulkheads

[FullSend]

I purchased an external overflow box from Fuji Cube. It looks great! Just one thing, I can not thread the nut onto the smaller bulkheads. It is unbelievably tight. Of the three, on one of them I could possibly thread the nut all the way onto the bulkhead. On the other two, I can get two or three threads max, even if I use channel locks.

Has anyone had this experience?

Is there a lubricant I can use on plastic?

 

[zoomonster]

Not clear the real issue. I assume you know all the Fiji stuff is metric and you are not mixing and matching bulkheads and nuts. I recently bought a used Fiji 32 int and went through hell trying to get bulkheads that would work. If those nuts don't go on easily something is wrong/mismatched.