CIRCLIP EXT 18 X 1.2

External Circlip  

18 x 1.2mm  

To measure a circlip whether its External or Internal you would measure from the Outside on One side to the Inside on the Other across the widest point on the circlip.   

This would give you the shaft bore size.   

So if you are measuring 55mm across this point then your shaft bore size should be 55mm also.