On offer are M4 Rubber Washers, choose from 17 different sizes and from pack size 2, 10, 50, 200 and 500 Washers.  
Dimensions in millimetres (mm):

OUTSIDE DIAMETER (O/D) X INSIDE DIAMETER (I/D) X THICKNESS

8 X 4.6 X 0.8
8.6 X 4.4 X 1.2
9 X 4.5 X 0.6
9 X 4.1 X 1.6
9.3 X 4 X 1.2
WHITE 9.8 X 4.3 X 1.6 
9.8 X 4.8 X 4
11.2 X 4 X 1.4
11.7 X 4.8 X 2
12 X 4.6 X 1.6
14.2 X 4.4 X 3
18.5 X 4 X 321 X 4.5 X 325.2 X 4.8 X 3.2
30 X 4.5 X 1.6
31.8 X 4.5 X 3.2  

Please send a message if you would like an item to be sent outside of the U.K.