I got another question regarding our Shingeki no Kyojin costumes via tumblr and I want to share my answer here too:

Question: What buckles did you use to attach the y-straps to the main (waist) belt? I can't figure out how to get the buckles through the main belt at all.

Those are actually normal buckles (a bit longer tough). Since we used real army belts (those with two holes in a row and consisting of really thick leather) we too had no idea how to attach them at first. But Majin thought of a simple trick.

THE Trick with removable Gear-Straps

She sewed two loops of fake-leather and fixed the buckle with the upper loop. The loop beneath fits on the belt perfectly and tadaaaaa~ you are able to remove it completely when needed. :) It is just noticable if you look closely.