Threads
Internal threads can be molded directly into the component using unscrewing cores. These mold features and functions are costly to produce, and as a result, are only applicable to high volume applications. For lower volume part applications, conventional tapping operations can be employed.
External threads can be molded directly onto the component thus eliminating the need for secondary thread-forming operations. Molding external threads is almost always a more cost effective approach than forming the threads with a secondary operation. Generally, a small flat, typically .005", at the parting line should be incorporated into the design. The recessed flat, shown in Fig. 17, will insure proper mold seal-off and reduce the opportunity for parting-line vestige to interfere with component function. Without the presence of a flat along the parting-line, you can expect problems with flash to develop in the root of the threads within the production of very few parts. This will likely increase tooling maintenance and down time.
