Compression springs of different measurements, with the effective resulting resistances that I've measured for them (when inserted to Gamecube controller triggers) marked for each type.
Original trigger springs have around 130 gf resistance, with some variation between production batches (usually 125-135 gf). Most people prefer slightly lower resistances for Melee, with the 90-100 gf range usually being the sweetspot for regular trigger configurations.
The really low resistance springs (40gf, 50gf and 60gf) are really soft and will make accidental lightshield inputs in Melee quite likely when combined with regular trigger setups and resting your finger on the trigger (as opposed to hovering above whenever not intending to press the trigger).
I find these more useful when coupled with digital-only trigger setups, such as with max-length trigger plugs (optionally with mouse click switches), where they allow for tweaking the total resistance very carefully.
The springs with higher resistance than default (140gf and 160gf) are meant for people who find the default springs too light, or for people who set up their triggers in the "domeless" configuration, where the center carbon cylinder of the click pad is cut out of the outer ring and glued to the bottom of the grey trigger piece or a trigger plug inserted there. (This configuration completely removes the click resistance that's usually around 360gf, so for people who rest their fingers on the triggers, it can be good to have just a bit more resistance to avoid accidental inputs.)
