What, exactly, are these and what function do they provide on flash hiders?  Do these function as "locking" devices to keep flash hiders secure on their threads?

What is the difference between a "crush" and "peel" washer (they both seem to fill the same function).  Thanks.

The crush washer for the FS is just a coned shaped washer that compresses when tighten.  On this type of washer, you simple hand tighten, then spin the FS to the correct index. This type of washer is a one time use, and if you don't watch what your doing, you can over spin the FS past the index point, which will require you to use a new crush washer.

On the peel type, the washer has layers that you can remove.  On this type, you remove layers until you can get the FS around 15* off index, then finish tightening the FS to index.

The washer is used to index the FS angled ports on the barrel.

note that some FS such as the vortex supposedly don't need to be indexed.

The Phantom is also one that doesn't need to be indexed, right?

Okay, I have another dumb question.  Can someone define "indexing" for me, as it relates to a flash hider?

On a FS, if you have the top slot in line with the top of the barrel, when you fire the weapon at night, the top slot will white out your sight picture.  The correct location/index of the top slot is at 1:00.

When using a brake, you want the side ports to be 3:00 and 9:00 from the top of the barrel.  The washer allows you to set the brake/FS to the correct position/"index" on the barrel, Verses having to take metal off the FS/brake to make it attach/mate in the correct orientation on the barrel when tightened.