Determination of the Fourth Digit for Injection Molded and Die Cast Parts

(Used under permission of Dixon and Poli,
Engineering Design and Design for Manufacturing)


The determination of this digit depends solely on whether or not the part has extensive external undercuts. A part is considered to have extensive external undercuts if the external undercuts are caused by features other than circular, unidirectional holes.

The following figure gives examples of both types of parts:

Parts without extensive external undercuts have a fourth digit value of 0.

Parts with extensive external undercuts have a fourth digit value of 1.