OK guys this might seem pretty ignorant but I shoot GT 5575 Trads with the standard GT insert.  I see screw in broadheads in 5/16ths or 11/16ths (ie. Zwickey Eskilite 135 gr. and Zwickey Eskimo 160 gr.).  Will they both fit my arrows?  What is the purpose of the 5/16ths vs. the 11/16ths?

I think those are wood shaft glue on broadheads you are looking at!!!

That is what I thought at first but I have double and triple checked.  On the Hidden E Outdoors website under the screw in broadheads for Zwickey they have the 135 gr. screw ins at 5/16ths and the 160 gr. screw ins at 11/32nds.

go 11/32       5

The threaded portion is the same on those the diameter on the ferrule is what it's talking about.  Two key just took their glue one models and put aluminum adapters in them.  The small is the black diamond and the larger is probably the delta or Eskimo.

Thanks, that make sense regarding the diameter of the ferrule.