The right tool(s) for the job...
The Alpha Primary Seal Ring (PSR)
The PSR application is a proprietary design. No other flashlight manufacturer on earth uses this method...unless it's a copy. The rings are custom made for this application by Smalley Steel Ring Compay in Lake Zurich, Illinois.
The PSR is now standard equipment on all Prometheus Alpha lights.
If you have an older Alpha and want to upgrade to the PSR, you can return the light to me, or you can buy this kit and install yourself. Check out the video below so you can see the process and decide if you want to tackle the upgrade or not.
Nylon Replaceable-Jaw Pliers
These are the same pliers that I use to assemble every Alpha. I tried about a dozen different approaches before I found this one, and it's perfect. If you watch my video below, you will see me using and old technique with the old bent-nose pliers I used to sell. These pliers make it super easy because A) you won't risk scratching your light and B) you can clamp down on the PSR and rotate the head to seat the ring, instead of moving the pliers around the rim (like in the video). Some day I'll get around to updating the video.
The jaws will become slightly damaged by the PSR with each use. You should be able to install the ring 5-10 times before they wear out. However, you can buy spare sets of jaws if you want to be sure you have a working tool when you need it.
Remove the PSR With the O-Ring Pick (photo below)
You won't need the pick to install the PSR, but you'll need it to get the PSR back out once it's installed. Either "pick-type" tool that I sell will work. If you got the Journeyman kit, it already comes with an o-ring pick. However, if you are buying the PSR upgrade and don't already have a pick, you can select the "full" kit from the dropdown menu on the right.
How-To: Remove and Install the PSR