Fittings and Valves. Global Top 3. Customers around the world love DK-LOK’s instrumentation fittings and valves for their consistent and impeccable quality. DK-LOK meticulously manages its product quality through statistical process control. We check product consistency by measuring critical dimensions with datum gauges periodically resulting in less than 10 faulty units for every 1 million fittings. We also performed complete intermix test where we tested all the intermix combinations with the biggest competitor fittings where we received 3rd party certification from TUV Rheinland showing no leakage during 2-year long test showing no leakage. Skills when honed for a long time fosters expertise and expertise is always the core element of perfect quality. DK-LOK makes and the world uses DK-LOK.