More details on how blade holder is designed?

[A Pieroway]

I am new to this. As are a lot of us I see..
Before I fill up my shopping cart, I could use a bit more information on blade holder options.
For the record, my first build will be an attempt to convert a Graflex flash (i own two, that I picked up 20 years ago in my twenties). I'm ready to do cool things with them now. I look forward to my first duel with my son. He's three now, but he'll grow up eventually.
None of the photos, tutorials, or videos from builds by other seem to cover the details of the blade holders. And, I've seen a LOT of them.
I'm guessing they're so basic a design that poeple just gloss over them.
I'm trying to figure out what is inside the holes on either end of them.
In particular, what's on the other far end of this $32 holder (see image attached or this url http://www.thecustomsabershop.com/As...EDgraflexa.JPG) ? It appears to be the only blade holder option I have for the Graflex, but I want/need to know for sure how the LED will sit in it before I'm comfortable buying one. What keeps the LED from moving around in the hilt?
Any diagrams, detailed photos, whatever that anyone can point me too that I may have missed. I'm looking for details. And, if I don't get it before I buy it, I'll be certain to post a nice long description of what I find afterwards?

And, on that part, can anyone describe better what the following in red means to me?
"LED graflex adapter for converting your Graflex to a LED saber. Anodized black. Designed to hold a 1" OD blade. The three 4-40 holes on the back do not match up to the chassis parts we sell. We will be offering some graflex specific chassis parts in the future."
Thanks
Al

LEDgraflexa.JPG