There are two designs that compress Silicone differently :
White GL base have more room for the silicone to flex for smooth operation. Good for overall setups.
Black GL base have better stability, but it will slightly add more tension. Good for low tension setups.
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Based on switch spacing, there are two options:
Fixed Spacing is traditional mounting method where all the switches have same distance/spacing. Good for user who prefer simplicity.
Variable Spacing, it allows user positioning switch individually, to adjust sensitivity for each directions. Good for user who like tuning lever. Switch Spacer needed to set the switches spacing (sold separately).
*All necessary screws are included on every GL base.