These springrests are intended for those trying to convert a recon, raider, or OG Alpha Trooper to a direct plunger internal system. One of these is designed to fit the recon and raider (snugger fit in the former), while the other is sized specifically for the Alpha trooper (Which as always has to be the special child)
These should work with stock springloads as well as upgrade springs. I have tested up to 9kg with no issues, but do not have anything stronger on hand to test with.
The author marked this model as their own original creation.