Accessories and valves. Global Top 3. Customers around the world love DK-LOK instrumentation valves and fittings for their consistent and flawless quality. DK-LOK meticulously manages the quality of its product through statistical process control. We verify product consistency by periodically measuring critical dimensions with reference gauges, resulting in fewer than 10 defective units per million accessories. We also did a complete mix test where we tested all mix combinations with the largest competition accessories where we received the third best competitor certification from TUV Rheinland showing no leaks during the 2-year test. Long-honed skills foster experience, and experience is always the core element of perfect quality. DK-LOK does, and the world uses DK-LOK.