Try before you buy !
Purchase this sample pack and decide which size fits you better.
This "extended edition"
will also let the undecided or curious key clackers compare how hard O-rings feel vs softer ones ~
Includes five O-rings of each size (1.5mm / 2.5mm / 3mm) made from silicone and nitrile rubber, respectively with a Shore hardness of 40A and 70A.