19 Plastic Shrinkage and Sink Marks Fig.10.16 Most commonly can be seen opposite closure threads Sink marks over cup flange support ribs can cause sealing problems Intended design Shrinkage = fx Shrinkage = 4fx Actual part produced Sink mark 3x 4x X19 Plastic Shrinkage and Sink Marks Fig.10.16 Most commonly can be seen opposite closure threads Sink marks over cup flange support ribs can cause sealing problems Intended design Shrinkage = fx Shrinkage = 4fx Actual part produced Sink mark 3x 4x X