3 lb - for use with polished strikers and very soft primers
3.5 lb - for competition, lightens the trigger and maintains excellent percussion on the primer
4 lb - to improve the trigger, but requires reliability in all conditions
 
Compatibility:
Glock 17/34 gen 3
Glock 17/34 gen 4
Glock 17/34 gen 5
Glock 19 gen 3
Glock 19 gen 4
Glock 19 gen 5
Glock 19X
Glock 45