I can't say how the fit is on the id of the outer spring (can't tell for sure from the pic), but the od only needs to be a minimum of the springs mean diameter (middle of the coil), Much larger than that is just added retainer weight, but they have got to be tight on the id to be that small. I've cut down and reprofiled steel retainers in the past and saved 8-10 grams each by making the od close to the spring mean diameter,

Mike Beachel

I didn't write the rules of math nor create the laws of physics, I am just bound by them.