BI-Lok Series D Dual Ferrule Tube Fittings are manufactured to be completely component intermixable with the Swagelok brand of tube fittings. Independent third party testing concluded that piece by piece intermixing of each manufacturer's component parts, in various combinations, yielded no performance degradation of the fitting connection. BI-Lok Dual Ferrule Tube Fittings are fully compatible for use with the Swagelok brand Gap Inspection Gauges. Need additional help? Call 800-264-7793 and we'll be happy to assist you with your BI-Lok needs.