Primary Arms does not state the diameter of the magnification ring on the Primary Arms PLX 6-30x56mm scope. I recommend measuring the outer diameter of the magnification adjustment or contacting Primary Arms for that information.
The Switchview Double Screw Folding Switchview may fit a Vortex Strike Eagle. However, you would need to know what model Strike Eagle you have.
I recommend using the Switchview Double Screw Folding Switchview model that is 1.65"-1.72". That is model number 1650-1720 DSFD.
IMHO... measure your Magnification Ring OD. Once you have that measurement you can order by measurement not by hear-say !
Personal opinion, slip the lever on your Mag Ring.
Look to see if there is an empty area where you can fold the lever when not in use.
If there is not space on your scope to fold the lever, this ring may not be the best one for your application.
My UTG 3-12x44 Scope has a space so the lever can fold back towards the eye piece when not in use and at the 3x mag location.
When using the Scope and the lever, it should be straight up and not able to scratch the Scope.
You would need this one: 3KM-RA-MATL-1762SV
The MPN:1650-1720 DSFD should fit that optic.
MPN: 1819-1870 DSFD should fit.
Since Nikon has discontinued the M308 riflescope, the specifications are no longer listed. You will need to measure the diameter of your magnification ring, and order the appropriate size.