I don't know about the Rubicon, but most Hondas take a 17mm allen. If you have trouble finding one, just find a bolt with that head size and stick the threaded part of the bolt inside a socket and weld it.

 

yeppers..most are 17mm allen head, don't worry about the outter lock nut part..as most just move when you loosen the inner allen head bolt part.

 

I have an 04 Rubi,and according to the manual(and working on other year Rubis) It is a 17mm allen,and you can usually pick one up on ebay for 12bux,having 2 of them makes it easier, one to hold one side,and another to turn the opposing side...