Sold in single quantities.
Fits:

K1.5-I
K2.5-1
K3.1
K4-1
K4-W
K6-1
K6-W
K8-1
K10-1
K12-1
V4.5-I
V4.5 W
V7-1
V7-W
V9-1
V9-W
V12-1
V12-W