Smalley L1 springs can be used as replacements for original Gamecube controller stickbox springs. Their force profile is substantially lower, so moving the stick takes considerably less force than with OEM or L2 springs.
My measurements, displayed as force-extension graphs, can be found here: Twitter post, which shows in-game input values (Melee levels) on the x-axis and force on the y-axis.
L1 springs should always be installed together with shim rings of 0.010-0.040 inch thickness inserted below the spring, otherwise with most stickboxes (except some brand new ones) the spring won't reliably return the stick all the way to the center.
These shim rings can be sourced in the US from McMaster-Carr in sets of 10s, and if you live in the US, I recommend that you buy them from there: [0.020"] [0.025"] [0.030"]
As an option for European and international customers or customers who want to get just a few to give them a try, I also offer sets of L1 springs plus individual shim rings.
Installing these into a stickbox is somewhat tricky, so buying these is recommended mainly if you already have experience with disassembling stickboxes.
These are made from carbon steel, so they should not get wet, otherwise rust is a possibility.
