DK-LOK® two ferrule tube fittings are raising the bar! DK-LOK® two ferrule tube fittings incorporate the most ROBUST, FULL MASS back ferrule technology on the market. This back ferrule technology along with outstanding dimensional control allows DK-LOK® to perform leak free against ASTM F-1387 as a pure assembly and when intermixed with Swagelok®. Ask us about our ASTM F-1387 pure and Intermix testing. Simply Impressive!