Preloading and Locking Core Pull Cylinders specifically designed for Injection Molds. Zero Flash Molded Parts on the First Shot! There is only one KOR-LOK® – if you’re not talking to PFA you’re not getting a KOR-LOK®. With 100% preload at ZERO pressure and fast Delivery on ANY STROKE size, you are just learning about what KOR-LOK® can do for you.