Hello all, I just sent off for an SP1 flash hider, from these people here:

https://rouschsports.com/shop/ar15-upper-parts/muzzle-devices-muzzle-brake-flash-hider-concussion-device/3-prong-flash-hider-sp1-retro/

It doesn't seem to be cut for a wrench. How are these things installed? I did a search and someone said "put a screwdriver between the prongs" (but that was the only tip I could find.)

Also, it's aligned with one of the slots 'up'?  

I also got this birdcage from brownells in case the sp1 doesn't work out.
http://www.brownells.com/rifle-parts/muzzle-devices/flash-hiders/ar-15-a2-flash-suppressor-22-cal-prod21246.aspx

It says it wants a peel washer. Any reason I can't use a crush washer? Peels are hard to find it seems.

The "Improved 3-Prong" FH was installed with a special wrench that fits between the prongs, but they sometimes damage the edges, so most of us simply install them with a strap wrench.
As for washers, you'll want a lock washer, not a crush or peel washer.
And finally, don't worry about indexing the FH.  It might look nicest with one prong at 6 o'clock and a gap at the top, but they were not designed with that in mind.

ETA: The "birdcage" you link to is actually an A2-style FH, and it would be indexed with the closed portion at the bottom.  That is a much newer design than the 3-prong.

Gunner filled you in on the info but let me give you a tip...fine a piece of metal (I have a flat piece of stainless steel that I randomly had in my garage) that fits between the prongs. I wrapped it heavily in painters tape and then used that to torque the 3 prong down. Don't over think it and you should be good to go.

This is what the wrench looked like.

Arg. I just order crush washers. Well, they don't cost much, but were all I could find. :(

Also, just to say, I'm not going for a full retro build, just a look-alike by renovating an old AWban bushmasher a2 with a new pencil barrel from brownell and a set of A1 furniture. (And a hyper modern trigger.)